Display systems and methods for determining registration between a display and a user&#39;s eyes

ABSTRACT

A wearable device may include a head-mounted display (HMD) for rendering a three-dimensional (3D) virtual object which appears to be located in an ambient environment of a user of the display. The relative positions of the HMD and one or more eyes of the user may not be in desired positions to receive, or register, image information outputted by the HMD. For example, the HMD-to-eye alignment vary for different users and may change over time (e.g., as a given user moves around or as the HMD slips or otherwise becomes displaced). The wearable device may determine a relative position or alignment between the HMD and the user&#39;s eyes. Based on the relative positions, the wearable device may determine if it is properly fitted to the user, may provide feedback on the quality of the fit to the user, and may take actions to reduce or minimize effects of any misalignment.

PRIORITY CLAIM

This application is a continuation application of U.S. patentapplication Ser. No. 16/251,017, entitled “DISPLAY SYSTEMS AND METHODSFOR DETERMINING RESGISTRATION BETWEEN A DISPLAY AND A USER'S EYES” filedon Jan. 17, 2019, which claims priority to: U.S. Patent Prov. App.62/644,321, entitled “DISPLAY SYSTEMS AND METHODS FOR DETERMININGREGISTRATION BETWEEN A DISPLAY AND A USER'S EYES” and filed on Mar. 16,2018; U.S. Patent Prov. App. 62/618,559, entitled “EYE CENTER OFROTATION DETERMINATION, DEPTH PLANE SELECTION, AND RENDER CAMERAPOSITIONING IN DISPLAY SYSTEMS” filed on Jan. 17, 2018; and U.S. PatentProv. App. 62/702,849, entitled “EYE CENTER OF ROTATION DETERMINATION,DEPTH PLANE SELECTION, AND RENDER CAMERA POSITIONING IN DISPLAY SYSTEMS”and filed on Jul. 24, 2018. Each of the above-recited applications isincorporated herein by reference in its entirety.

INCORPORATION BY REFERENCE

This application incorporates by reference the entirety of each of thefollowing patent applications and publications: U.S. application Ser.No. 14/555,585 filed on Nov. 27, 2014, published on Jul. 23, 2015 asU.S. Publication No. 2015/0205126; U.S. application Ser. No. 14/690,401filed on Apr. 18, 2015, published on Oct. 22, 2015 as U.S. PublicationNo. 2015/0302652; U.S. application Ser. No. 14/212,961 filed on Mar. 14,2014, now U.S. Pat. No. 9,417,452 issued on Aug. 16, 2016; U.S.application Ser. No. 14/331,218 filed on Jul. 14, 2014, published onOct. 29, 2015 as U.S. Publication No. 2015/0309263; U.S. PatentPublication No. 2016/0270656; U.S. Patent Publication No. 2015/0178939,published Jun. 25, 2015; U.S. Patent Publication No. 2015/0016777; U.S.patent application Ser. No. 15/274,823; U.S. patent application Ser. No.15/296,869; U.S. patent application Ser. No. 15/717,747, filed Sep. 27,2017; U.S. patent application Ser. No. 15/497,726, filed Apr. 26, 2017;U.S. Patent Publication No. 2017/0053165, published Feb. 23, 2017; U.S.Patent Publication No. 2017/0053166, published Feb. 23, 2017; U.S.application Ser. No. 15/341,760, filed on Nov. 2, 2016, published on May4, 2017 as U.S. Publication No. 2017/0122725; U.S. application Ser. No.15/341,822, filed on Nov. 2, 2016, published on May 4, 2017 as U.S.Publication No. 2017/0124928; U.S. Provisional Patent Application No.62/618,559, filed Jan. 17, 2018; and U.S. Provisional Patent ApplicationNo. 62/642,761, filed Mar. 14, 2018.

FIELD

The present disclosure relates to display systems, including virtualreality and augmented reality display systems, and, more particularly,to systems and methods for evaluating fit of a display on a user.

BACKGROUND

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality”, “augmentedreality”, or “mixed reality” experiences, wherein digitally reproducedimages or portions thereof are presented to a user in a manner whereinthey seem to be, or may be perceived as, real. A virtual reality, or“VR”, scenario typically involves presentation of digital or virtualimage information without transparency to other actual real-world visualinput; an augmented reality, or “AR”, scenario typically involvespresentation of digital or virtual image information as an augmentationto visualization of the actual world around the user; a mixed reality,or “MR”, related to merging real and virtual worlds to produce newenvironments where physical and virtual objects co-exist and interact inreal time. As it turns out, the human visual perception system is verycomplex, and producing a VR, AR, or MR technology that facilitates acomfortable, natural-feeling, rich presentation of virtual imageelements amongst other virtual or real-world imagery elements ischallenging. Systems and methods disclosed herein address variouschallenges related to VR, AR and MR technology.

SUMMARY

Various examples of registration observation and response in a mixedreality system are disclosed.

In some embodiments, a display system is provided for projecting lightto an eye of a user to display virtual image content. The display systemcomprises a frame configured to be supported on a head of the user, ahead-mounted display disposed on the frame, the display configured toproject light into the user's eye to display virtual image content withdifferent amounts of wavefront divergence to present virtual imagecontent appearing to be located at different depths at different periodsof time, one or more eye-tracking cameras configured to image the user'seye, and processing electronics in communication with the display andthe one or more eye-tracking cameras. The processing electronics areconfigured to determine a position of the eye based on images of the eyeobtained with the one or more eye-tracking cameras, determine whetherthe position of the eye is within a display registration volume of thehead-mounted display system, and provide a notification based ondetermining whether the position of the eye is within the displayregistration volume, where the notification indicates at least that thedisplay and the eye are not properly registered.

In some other embodiments, a display system is configured to projectlight to an eye of a user to display virtual image content. The displaysystem comprises a frame configured to be supported on a head of theuser; a head-mounted display disposed on the frame, the displayconfigured to project light into the user's eye to display virtual imagecontent with different amounts of wavefront divergence to presentvirtual image content appearing to be located at different depths atdifferent periods of time; one or more eye-tracking cameras configuredto image the user's eye; and processing electronics in communicationwith the display and the one or more eye-tracking cameras. Theprocessing electronics are configured to: determine a position of theeye based on images of the eye obtained with the one or moreeye-tracking cameras; determine whether the position of the eye is morethan a first threshold distance outside of a viewing volume of thehead-mounted display system; and in response to a determination that theposition of the eye is more than the first threshold distance outside ofthe viewing volume of the head-mounted display system, provide feedbackto the user indicating that the display and the eye are not properlyregistered for output.

In some other embodiments, a display system is provided for projectinglight to an eye of a user to display virtual image content. The displaysystem comprises a frame configured to be supported on a head of theuser, a head-mounted display disposed on the frame, the displayconfigured to project light into the user's eye to display virtual imagecontent with different amounts of wavefront divergence to presentvirtual image content appearing to be located at different depths atdifferent periods of time, one or more eye-tracking cameras configuredto image the user's eye, and processing electronics in communicationwith the display and the one or more eye-tracking cameras. Theprocessing electronics are configured to determine whether the lightprojected by head-mounted display is properly registered by the eye ofthe user and provide feedback to the user if the head-mounted display isnot properly adjusted to fit the user to register the light projected bythe display system.

In yet other embodiments, a method is provided for evaluatingregistration of virtual image content from a head-mounted display systemby a user's eye. The method comprises determining a first position ofthe eye, determining whether the first position of the eye is within adisplay registration volume of the head-mounted display system, wherethe display registration volume is an imaginary volume associated withproper fit of the head-mounted display system relative to the user'seye, and providing a notification based on determining whether theposition of the eye is within the display registration volume, where thenotification indicates at least that the display and the eye are notproperly registered.

Additional examples of embodiments are enumerated below.

Example 1. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content with different amounts of wavefront        divergence to present virtual image content appearing to be        located at different depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   determine a position of the eye based on images of the eye            obtained with the one or more eye-tracking cameras;        -   determine whether the position of the eye is within a            display registration volume of the head-mounted display            system; and        -   provide a notification based on determining whether the            position of the eye is within the display registration            volume, where the notification indicates at least that the            display and the eye are not properly registered.

Example 2. The display system of Example 1, wherein the processingelectronics are further configured to, upon determining that theposition of the eye is outside of the display registration volume,provide feedback to the user that the head-mounted display is notproperly adjusted to fit the user, wherein the feedback is thenotification provided based on determining whether the position of theeyes within the display registration volume.

Example 3. The display system of Example 1, further comprising at leastone interchangeable fit piece removably mounted to the frame andconfigured to adjust a fit of the frame.

Example 4. The display system of Example 3, wherein the interchangeablefit piece comprises an interchangeable nose bridge configured to adjustthe fit of the frame between the frame and a nose bridge of the user.

Example 5. The display system of Example 3 or 4, wherein theinterchangeable fit piece comprises an interchangeable forehead padconfigured to adjust the fit of the frame between the frame and aforehead of the user.

Example 6. The display system of any of Examples 3 to 5, wherein theinterchangeable fit piece comprises an interchangeable back padconfigured to adjust the fit of the frame between the frame and a backof the head of the user.

Example 7. The display system of any of Examples 2 to 6, wherein theprocessing electronics is further configured such that providing thenotification comprises providing feedback to the user that thehead-mounted display is not properly adjusted to fit the user comprisesproviding a suggestion to the user to swap out a currently-installedinterchangeable fit piece for another interchangeable fit piece.

Example 8. The display system of any of Examples 1 to 7, furthercomprising one or more light sources disposed on the frame with respectto the user's eye to illuminate the user's eye, the one or moreeye-tracking cameras forming images of the eye using the light from theone or more light sources.

Example 9. The display system of Example 8, wherein the one or morelight sources comprises at least two light sources disposed on the framewith respect to the user's eye to illuminate the user's eye.

Example 10. The display system of any of Examples 8 to 9, wherein theone or more light sources comprises infrared light emitters.

Example 11. The display system of any of Examples 8 to 10, wherein oneor more light sources form one or more glints on the eye and theprocessing electronics is configured to determine a location of thecornea based on the one or more glints.

Example 12. The display system of any of Examples 1 to 11, wherein theposition of the eye it is a location of a center of rotation of the eye.

Example 13. The display system of any of Examples 1 to 11, wherein thecornea has associated therewith a cornea sphere having a center ofcurvature and the processing electronics is configured to determine alocation of the center of curvature of the cornea sphere.

Example 14. The display system of Example 1, wherein the processingelectronics is configured to provide the notification by providinginstructions causing the display to boost a brightness of a plurality ofpixels of the display relative to other pixels of the display, whereinthe plurality of pixels with a boosted brightness comprise pixelsexpected to undergo perceived dimming under improper registration.

Example 15. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content with different amounts of wavefront        divergence to present virtual image content appearing to be        located at different depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   determine a position of the eye based on images of the eye            obtained with the one or more eye-tracking cameras;        -   determine whether the position of the eye is more than a            first threshold distance outside of a viewing volume of the            head-mounted display system; and        -   in response to a determination that the position of the eye            is more than the first threshold distance outside of the            viewing volume of the head-mounted display system, provide            feedback to the user indicating that the display and the eye            are not properly registered for output.

Example 16. The display system of Example 15, wherein the processingelectronics are configured to determine whether the position of the eyeis more than the first threshold distance outside of a viewing volume byat least:

-   -   determining whether the position of the eye is less than a        second threshold distance from the eyepiece; and    -   in response to a determination that the position of the eye is        less than the second threshold distance from the head-mounted        display system, providing feedback to the user indicating that        the display and the eye are not properly registered for output.

Example 17. The display system of Example 15, wherein the processingelectronics are configured to determine whether the position of the eyeis more than the first threshold distance outside of a viewing volume byat least:

-   -   determining whether the position of the eye is more than a        second threshold distance from the eyepiece; and    -   in response to a determination that the position of the eye is        more than the second threshold distance from the head-mounted        display system, providing feedback to the user indicating that        the display and the eye are not properly registered for output.

Example 18. The display system of Example 15, wherein the processingelectronics are configured to determine whether the position of the eyeis more than the first threshold distance outside of a viewing volume byat least:

-   -   determining whether the position of the eye is more than a        second threshold distance outside of a subspace of a field of        view of the eye tracking camera; and    -   in response to a determination that the position of the eye is        more than the second threshold distance outside of the subspace        of the viewing volume of the eye tracking camera, providing        feedback to the user indicating that the display and the eye are        not properly registered for output.

Example 19. The display system of Example 15 wherein the viewing volumeof the head-mounted display is a volume through which light representingevery pixel of virtual image content presented by the head-mounteddisplay is expected to pass.

Example 20. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content with different amounts of wavefront        divergence to present virtual image content appearing to be        located at different depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   determine whether the light projected by head-mounted            display is properly registered by the eye of the user; and        -   provide feedback to the user if the head-mounted display is            not properly adjusted to fit the user to register the light            projected by the display system.

Example 21. The display system of Example 20, further comprising atleast one interchangeable fit piece removably mounted to the frame andconfigured to adjust a fit of the frame.

Example 22. The display system of Example 21, wherein theinterchangeable fit piece comprises an interchangeable nose bridgeconfigured to adjust the fit of the frame between the frame and a nosebridge of the user.

Example 23. The display system of Example 20 or 22, wherein theinterchangeable fit piece comprises an interchangeable forehead padconfigured to adjust the fit of the frame between the frame and aforehead of the user.

Example 24. The display system of any of Examples 20 to 23, wherein theinterchangeable fit piece comprises an interchangeable back padconfigured to adjust the fit of the frame between the frame and a backof the head of the user.

Example 25. The display system of any of Examples 20 to 24, wherein theprocessing electronics is further configured such that providingfeedback to the user that the head-mounted display is not properlyadjusted to fit the user comprises providing a suggestion to the user toswap out a currently-installed interchangeable fit piece for anotherinterchangeable fit piece.

Example 26. A method for evaluating registration of virtual imagecontent from a head-mounted display system by a user's eye, the methodcomprising:

-   -   determining a first position of the eye;    -   determining whether the first position of the eye is within a        display registration volume of the head-mounted display system,        wherein the display registration volume is an imaginary volume        associated with proper fit of the head-mounted display system        relative to the user's eye; and    -   providing a notification based on determining whether the        position of the eye is within the display registration volume,        where the notification indicates at least that the display and        the eye are not properly registered.

Example 27. The method of Example 26, wherein the head-mounted displaysystem comprises an eye-tracking camera, wherein determining the firstposition of the eye comprises utilizing the eye-tracking camera to imagethe eye of the user.

Example 28. The method of Example 27, wherein the first position of theeye is a position of the center of rotation of the eye, and furthercomprising calculating a center of rotation of the eye based uponimaging of the eye by the eye-tracking camera.

Example 29. The method of Example 26, wherein the head-mounted displaysystem is configured to project light into the eye to display virtualimage content in the field of view of the user, and further comprisingdisplaying an indication that the wearable system is properly fitted.

Example 30. The method of any of Examples 26 to 29, further comprisingautomatically tracking the center of rotation of the eye over time withthe head-mounted display system and notify the user when the center ofrotation of the eye moves outside of the registration display volume.

Example 31. The method of Examples 26 or 29, further comprising:

-   -   determining a second position of the eye;    -   determining that the second position of the eye is within the        display registration volume; and    -   in response to determining that the second position of the eye        is within the display registration volume, providing additional        feedback to the user indicating that the wearable system is        properly fitted to the user.

Example 32. The method of any of Examples 26 to 31, wherein, when theeye of the user is not within the display registration volume, at leastsome pixels of the head-mounted display system are dimmed or invisibleto the user.

Example 33. The method of any of Examples 26 to 32, further comprisingchanging a field of view of the head-mounted display system when theposition of the eye is outside the display registration volume,

-   -   wherein the head-mounted display system comprises at least one        display having a first field of field when the position of the        eye is inside the display registration volume, wherein the        display has a second field of view when the position of the eye        is outside the display registration volume, and wherein the        second field of view is smaller than the first field of view.

Example 34. The method of Example 33, wherein providing the notificationcomprises providing feedback to the user within the second field ofview.

Example 35. The method of any of Examples 26 to 34, wherein the wearablesystem comprises at least one interchangeable fit piece, and furthercomprising:

-   -   providing a notification to the user indicating that the        wearable system is not properly fitted to the user,    -   wherein the notification comprises a suggestion or an        instruction to the user to replace a currently-installed        interchangeable fit piece with an alternative interchangeable        fit piece.

Example 36. The method of Example 35, wherein the interchangeable fitpiece comprises at least one fit piece selected from the groupconsisting of: a nose bridge pad, a forehead pad, and a back pad thatgoes between the wearable system and a back of a user's head.

Example 37. The method of Example 36, wherein the wearable systemcomprises at least one interchangeable nose bridge pad, furthercomprising determining that a display of the head-mounted system is toolow with respect to the eye, and wherein providing the notification tothe user comprises prompting the user to install a larger nose bridgepad.

Example 38. The method of any of Examples 26 to 37, further comprising:

-   -   identifying a plurality of pixels of a display of the        head-mounted display system that the user is expected to        perceive as dimmed as a result of the first position of the eye        being outside the display registration volume; and    -   boosting brightness of the plurality of pixels of the display        relative to other pixels in the display to mitigate the expected        dimming.

Example 39. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content as rendered by a virtual render camera        with different amounts of wavefront divergence to present        virtual image content appearing to be located at different        depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   determine a distance away from the display at which the eye            is located based on images of the eye obtained with the one            or more eye-tracking cameras, and        -   adjust a focal length of the virtual render camera based on            the determined distance.

Example 40. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content with different amounts of wavefront        divergence to present virtual image content appearing to be        located at different depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   determine a position of the eye relative to the display            based on images of the eye obtained with the one or more            eye-tracking cameras;        -   determine an amount of pixels of virtual image content that            the user is expected to perceive as dimmed based on the            position of the eye relative to the display; and        -   control operation of the display based on the determined            amount of pixels.

Example 41. The display system of Example 40, wherein the processingelectronics are configured to determine an amount of pixels of virtualimage content that the user is not expected to perceive as dimmed basedon the position of the eye relative to the display.

Example 42. The display system of Examples 40 or 41, wherein theprocessing electronics are configured to control operation of thedisplay by:

-   -   boosting a brightness of the pixels of virtual image content        that the user is expected to perceive as dimmed based on the        position of the eye relative to the display.

Example 43. The display system of any of the Examples 40-42, wherein theamount of pixels of virtual image content comprises a percentage ofpixels.

Example 44. The display system of any of the Examples 40-43, wherein theprocessing electronics are configured to compare the amount of pixels ofvirtual image content with one or more thresholds and, in response to adetermination that the amount of pixels of virtual image content exceedsone or more thresholds, provide feedback to the user indicating that thedisplay and the eye are not properly registered for output.

Example 45. A display system configured to project light to an eye of auser to display virtual image content, the display system comprising:

-   -   a frame configured to be supported on a head of the user;    -   a head-mounted display disposed on the frame, the display        configured to project light into the user's eye to display        virtual image content with different amounts of wavefront        divergence to present virtual image content appearing to be        located at different depths at different periods of time;    -   one or more eye-tracking cameras configured to image the user's        eye; and    -   processing electronics in communication with the display and the        one or more eye-tracking cameras, the processing electronics        configured to:        -   define a registration volume relative to the display based            on one or more parameters;        -   determine a position of the eye based on images of the eye            obtained with the one or more eye-tracking cameras;        -   determine whether the position of the eye is within the            registration volume of the head-mounted display system; and        -   control operation of the display based on determining            whether the position of the eye is within the display            registration volume.

Example 46. The display system of Example 45, wherein the one or moreparameters comprise a type of application that is running on the displaysystem.

Example 47. The display system of any of Examples 45-46, wherein the oneor more parameters comprise one or more physical parameters of thehead-mounted display.

Example 48. The display system of any of Examples 45-47, wherein the oneor more physical parameters of the head-mounted display comprise one ormore of a display field of view, a display surface size, a shape of thedisplay, an outer housing of the display, an amount of optical powerimparted by the display to light representing virtual image content.

Example 49. The display system of any of Examples 45-48, wherein theprocessing electronics are configured to control operation of thedisplay by presenting virtual image content to the user indicating atleast that the display and the eye are not properly registered.

Example 50. The display system of Example 15, wherein the processingelectronics are configured to determine whether the position of the eyeis more than the first threshold distance outside of the viewing volumeby at least:

-   -   determining whether the position of the eye is more than a        second threshold distance outside of a subspace of the viewing        volume of an outer housing of the head-mounted display; and    -   in response to a determination that the position of the eye is        more than the second threshold distance outside of the subspace        of the viewing volume of the outer housing of the head-mounted        display, providing feedback to the user indicating that the        display and the eye are not properly registered for output.

Example 52. The display system of Example 15, wherein the processingelectronics are further configured to:

-   -   identify an application running on the display system; and    -   determine the first threshold distance based on the identified        application.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed description purports to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustration of a mixed reality scenario with certainvirtual reality objects, and certain physical objects viewed by aperson.

FIG. 2 schematically illustrates an example of a wearable system.

FIG. 3 schematically illustrates example components of a wearablesystem.

FIG. 4 schematically illustrates an example of a waveguide stack of awearable device for outputting image information to a user.

FIG. 5 schematically illustrates an example of an eye.

FIG. 6 is a schematic diagram of a wearable system that includes an eyetracking system.

FIG. 7A is a block diagram of a wearable system that may include an eyetracking system.

FIG. 7B is a block diagram of a render controller in a wearable system.

FIG. 7C is a block diagram of a registration observer in a head-mounteddisplay system.

FIG. 8A is a schematic diagram of an eye showing the eye's cornealsphere.

FIG. 8B illustrates an example corneal glint detected by an eye-trackingcamera.

FIGS. 8C-8E illustrate example stages of locating a user's cornealcenter with an eye tracking module in a wearable system.

FIGS. 9A-9C illustrate an example normalization of the coordinate systemof eye tracking images.

FIGS. 9D-9G illustrate example stages of locating a user's pupil centerwith an eye tracking module in a wearable system.

FIG. 10 illustrates an example of an eye including the eye's optical andvisual axes and the eye's center of rotation.

FIG. 11 is a process flow diagram of an example of a method for usingeye tracking in rendering content and providing feedback on registrationin a wearable device.

FIGS. 12A and 12B illustrate a nominal position of a display elementrelative to a user's eye and illustrate a coordinate system fordescribing the positions of the display element and the user's eyerelative to one another.

FIGS. 13A and 13B illustrate nominal positioning and positioningtolerances of a display element relative to a user's eye in ahead-mounted display system.

FIGS. 13C and 13D illustrate a display registration volume and a user'seye viewing content from a display.

FIG. 14 illustrates an example of the perceived dimming of a display forvarious positions of a user's eye relative to the display.

FIGS. 15A and 15B are exploded perspective views of a head-mounteddisplay system having interchangeable pieces such as back pads, foreheadpads, and nose bridge pads to adjust fit of a head-mounted display ofthe display system for different users.

FIG. 16 is a process flow diagram of an example of a method forobserving registration and providing feedback on registration with ahead-mounted display system.

FIGS. 17A-17H illustrate views of light fields projected by a displayand how the intersections of the light fields may partly define adisplay registration volume.

FIG. 18 illustrates a top-down view of light fields projected by adisplay and how the intersections of the light fields may partly definea display registration volume.

FIG. 19A illustrates a registration volume derived from a displayhousing of a head-mounted display system.

FIG. 19B illustrates superimposed registration volumes of a displayhousing and a display of a head-mounted display system.

FIG. 19C illustrates an aggregate registration volume derived from thesuperimposed registration volumes of FIG. 19B.

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

DETAILED DESCRIPTION

The display portion of a display system may include a head-mounteddisplay (HMD) which may display a three-dimensional (3D) virtual objectsuch that the object appears to be located within the user's ambientenvironment. As a result, the 3D virtual object may be perceived by theuser in a similar manner as real world objects.

The HMD may display images by outputting spatially modulated light tothe user, with the light corresponding to the virtual object. Thespatially modulated light may contain image information may be referredto as image light. To be perceived by the user, the image light travelsfrom the HMD to an eye of the user, propagates through the pupil, andimpinges on the eye's retina. It will be appreciated that if all or aportion of the image light for an image does not enter the pupil of theeye and/or does not impinge on the eye's retina, then the viewer wouldnot see the image or the quality of the image may be degraded. As usedherein, registration relates to the relative positioning of the displayand the user's eyes. For example, a display may be said to be properlyregistered when the user's eyes and the display are positioned relativeto one another for a desired amount of image light to enter the eye. Aregistration observer (e.g., a computer program) in the display devicemay be programmed to monitor whether the display is properly registeredor positioned for the eye to receive the image light from the display.

In order to properly display content to users, e.g., by having theuser's eyes positioned to receive image light, the user's eyes may needto be situated within a particular region or volume of space relative tothe HMD. This volume may be referred to as the display registrationvolume. If the user's eyes are outside the display registration volume,display quality may be degraded (e.g., there may be dimming and/ordisplayed content that does not reach the users eyes). Various factorsmay combine to determine the positions of the user's eyes relative tothe HMD and thus whether the user's eyes are situated within the desireddisplay registration volume. As an example, anatomical variationsbetween users may mean that the head-mounted display fits some users ina manner that places their eyes outside the display registration volume.As another example, the HMD may not be rigidly affixed to a user's headand may shift on the user's head over time, particularly when the useris moving around. As particular examples, the HMD may slip down theuser's nose or tilt relative to a line (the interocular axis) betweenthe user's eyes and, as a result, the HMD may not be able to providedesired virtual content (e.g., without some undesirable degradation) dueto the shift of the display relative to the user's eyes.

Various systems and techniques described herein are at least in partdirected to solving problems related to proper registration of a displayto allow the viewer to view image content as desired. In someembodiments, a head-mounted display system may be configured todetermine the position of an eye of the user. The display system maythen determine whether the position of that eye is within a displayregistration volume of the head-mounted display system. Determining theposition of the eye may include determining the position of arepresentative pointer volume associated with the eye e.g., the centerof rotation of the eye. Determining whether the position of the eye iswithin the display registration volume may include determining whetherthe center of rotation of the eye is within the display registrationvolume. As discussed herein, the center of rotation of the eye may bedetermined using an inward-facing imaging system configured to image theeye. In addition, in some embodiments, the display registration volumeis an imaginary volume associated with proper fit of the head-mounteddisplay system relative to the user's eye. For example, the displayregistration volume may be a volume defined by a projection from thesurface of the head-mounted display system outputting image light. Morespecifically, the display registration volume may be a three-dimensionalgeometric shape that tapers from a base towards an apex. The shape ofthe display registration volume's base may be defined at least in partby the geometry of the display, and the depth of the displayregistration volume (i.e., the distance from base to apex on the z-axis)may be at least in part defined by the field of view (FOV) of thedisplay. For example, a round or circular display (e.g., the shape ofthe area on a surface from which image light is outputted to the viewer)may yield a conical display registration volume, and a polygonal displaymay yield a pyramidal display registration volume. As an additionalexample, a display with a larger FOV may yield a display registrationvolume having a smaller depth than a display with a smaller FOV. In someembodiments, the display registration volume may have the general shapeof a truncated cone or pyramid. For example, the display registrationvolume may have the general shape of a frustum, e.g., a frustum of apyramid such as a rectangular pyramid.

In some embodiments, an inward-facing imaging system of the head-mounteddisplay system may acquire images of the user's face, including theireyes. The inward-facing imaging system may be an eye-tracking system,which may be mounted on a frame of the head-mounted display. Thehead-mounted display system may analyze the images to determine therelative position of the user's eyes and the HMD, and whether theposition of each of the user's eyes falls within the displayregistration volume for that eye. Based on this information, thehead-mounted display system may notify the user to adjust the fit of theHMD. For example, the notification may inform the user that the devicehas slipped and needs adjustment or a suggestion to make an adjustmentof the HMD. In at least some embodiments, the head-mounted displaysystem may take steps to mitigate any display degradation caused bymisalignment of the HMD to the user, such as by boosting brightness orlight output to the user in areas that would otherwise be dimmed bymisalignment or by moving virtual content. Accordingly, such embodimentsof the HMD may assist users with properly fitting the HMD and mitigatingissues caused by improper fit of the HMD, such as when the HMD slips,moves, or tilts relative to the user's head. In some embodiments, itwill be appreciated that the display system may be configured to notifythe user of misalignment and to also take steps to mitigate displaydegradation caused by the misalignment. In some other embodiments, thedisplay system may not provide a notification to the user; rather, thenotification may simply be instructions or flags within the displaysystem which trigger the display system to conduct actions to mitigateimage degradation caused by misalignment.

Advantageously, the analysis of registration may be performedautomatically utilizing images acquired from the inward-facing imagingsystem and information regarding the display registration volume storedor accessible by the display system. As a result, the fit of the HMD maybe corrected upon first using the HMD, and optionally also during thecourse of continued usage of the HMD to ensure a high level of imagequality in the use of the head-mounted display system.

Accordingly, a variety of implementations of systems and methods forobserving registration of a head-mounted display system and takingaction in response to the observed registration are provided herein.

Examples of 3D Display of a Wearable System

Reference will now be made to the drawings, in which like referencenumerals refer to like parts throughout. Unless indicated otherwise, thedrawings are schematic and not necessarily drawn to scale.

A wearable system (also referred to herein as a head-mounted displaysystem or as an augmented reality (AR) system) may be configured topresent 2D or 3D virtual images to a user. The images may be stillimages, frames of a video, or a video, in combination or the like. Atleast a portion of the wearable system may be implemented on a wearabledevice that may present a VR, AR, or MR environment, alone or incombination, for user interaction. The wearable device may be usedinterchangeably as an AR device (ARD). Further, for the purpose of thepresent disclosure, the term “AR” is used interchangeably with the term“MR”.

FIG. 1 depicts an illustration of a mixed reality scenario with certainvirtual reality objects, and certain physical objects viewed by aperson. In FIG. 1, an MR scene 100 is depicted wherein a user of an MRtechnology sees a real-world park-like setting 110 featuring people,trees, buildings in the background, and a concrete platform 120. Inaddition to these items, the user of the MR technology also perceivesthat he “sees” a robot statue 130 standing upon the real-world platform120, and a cartoon-like avatar character 140 flying by which seems to bea personification of a bumble bee, even though these elements do notexist in the real world.

In order for the 3D display to produce a true sensation of depth, andmore specifically, a simulated sensation of surface depth, it may bedesirable for each point in the display's visual field to generate anaccommodative response corresponding to its virtual depth. If theaccommodative response to a display point does not correspond to thevirtual depth of that point, as determined by the binocular depth cuesof convergence and stereopsis, the human eye may experience anaccommodation conflict, resulting in unstable imaging, harmful eyestrain, headaches, and, in the absence of accommodation information,almost a complete lack of surface depth.

VR, AR, and MR experiences may be provided by display systems havingdisplays in which images corresponding to a plurality of depth planesare provided to a viewer. The images may be different for each depthplane (e.g., provide slightly different presentations of a scene orobject) and may be separately focused by the viewer's eyes, therebyhelping to provide the user with depth cues based on the accommodationof the eye required to bring into focus different image features for thescene located on different depth plane or based on observing differentimage features on different depth planes being out of focus. Asdiscussed elsewhere herein, such depth cues provide credible perceptionsof depth.

FIG. 2 illustrates an example of wearable system 200 which may beconfigured to provide an AR/VR/MR scene. The wearable system 200 mayalso be referred to as the AR system 200. The wearable system 200includes a display 220, and various mechanical and electronic modulesand systems to support the functioning of display 220. The display 220may be coupled to a frame 230, which is wearable by a user, wearer, orviewer 210. The display 220 may be positioned in front of the eyes ofthe user 210. The display 220 may present AR/VR/MR content to a user.Because the display 220 may be configured to be worn on the head of theuser 210, it may also be referred to as a head-mounted display (HMD) andthe wearable system 200, comprising the display 220, may also bereferred to as a head-mounted display system.

In some embodiments, a speaker 240 is coupled to the frame 230 andpositioned adjacent the ear canal of the user (in some embodiments,another speaker, not shown, is positioned adjacent the other ear canalof the user to provide for stereo/shapeable sound control). The display220 may include an audio sensor (e.g., a microphone) 232 for detectingan audio stream from the environment and capture ambient sound. In someembodiments, one or more other audio sensors, not shown, are positionedto provide stereo sound reception. Stereo sound reception may be used todetermine the location of a sound source. The wearable system 200 mayperform voice or speech recognition on the audio stream.

The wearable system 200 may include an outward-facing imaging system 464(shown in FIG. 4) which observes the world in the environment around theuser. The wearable system 200 may also include an inward-facing imagingsystem 462 (shown in FIG. 4) which may track the eye movements of theuser. The inward-facing imaging system may track either one eye'smovements or both eyes' movements. The inward-facing imaging system 462may be attached to the frame 230 and may be in electrical communicationwith the processing modules 260 or 270, which may process imageinformation acquired by the inward-facing imaging system to determine,e.g., the pupil diameters or orientations of the eyes, eye movements oreye pose of the user 210. The inward-facing imaging system 462 mayinclude one or more cameras. For example, at least one camera may beused to image each eye. The images acquired by the cameras may be usedto determine pupil size or eye pose for each eye separately, therebyallowing presentation of image information to each eye to be dynamicallytailored to that eye.

As an example, the wearable system 200 may use the outward-facingimaging system 464 or the inward-facing imaging system 462 to acquireimages of a pose of the user. The images may be still images, frames ofa video, or a video.

The display 220 may be operatively coupled 250, such as by a wired leador wireless connectivity, to a local data processing module 260 whichmay be mounted in a variety of configurations, such as fixedly attachedto the frame 230, fixedly attached to a helmet or hat worn by the user,embedded in headphones, or otherwise removably attached to the user 210(e.g., in a backpack-style configuration, in a belt-coupling styleconfiguration).

The local processing and data module 260 may comprise a hardwareprocessor, as well as digital memory, such as non-volatile memory (e.g.,flash memory), both of which may be utilized to assist in theprocessing, caching, and storage of data. The data may include data a)captured from sensors (which may be, e.g., operatively coupled to theframe 230 or otherwise attached to the user 210), such as image capturedevices (e.g., cameras in the inward-facing imaging system or theoutward-facing imaging system), audio sensors (e.g., microphones),inertial measurement units (IMUs), accelerometers, compasses, globalpositioning system (GPS) units, radio devices, or gyroscopes; or b)acquired or processed using remote processing module 270 or remote datarepository 280, possibly for passage to the display 220 after suchprocessing or retrieval. The local processing and data module 260 may beoperatively coupled by communication links 262 or 264, such as via wiredor wireless communication links, to the remote processing module 270 orremote data repository 280 such that these remote modules are availableas resources to the local processing and data module 260. In addition,remote processing module 280 and remote data repository 280 may beoperatively coupled to each other.

In some embodiments, the remote processing module 270 may comprise oneor more processors configured to analyze and process data or imageinformation. In some embodiments, the remote data repository 280 maycomprise a digital data storage facility, which may be available throughthe internet or other networking configuration in a “cloud” resourceconfiguration. In some embodiments, all data is stored and allcomputations are performed in the local processing and data module,allowing fully autonomous use from a remote module.

Example Components of a Wearable System

FIG. 3 schematically illustrates example components of a wearablesystem. FIG. 3 shows a wearable system 200 which may include a display220 and a frame 230. A blown-up view 202 schematically illustratesvarious components of the wearable system 200. In certain implements,one or more of the components illustrated in FIG. 3 may be part of thedisplay 220. The various components alone or in combination may collecta variety of data (such as e.g., audio or visual data) associated withthe user of the wearable system 200 or the user's environment. It shouldbe appreciated that other embodiments may have additional or fewercomponents depending on the application for which the wearable system isused. Nevertheless, FIG. 3 provides a basic idea of some of the variouscomponents and types of data that may be collected, analyzed, and storedthrough the wearable system.

FIG. 3 shows an example wearable system 200 which may include thedisplay 220. The display 220 may comprise a display lens 226 that may bemounted to a user's head or a housing or frame 230, which corresponds tothe frame 230. The display lens 226 may comprise one or more transparentmirrors positioned by the housing 230 in front of the user's eyes 302,304 and may be configured to bounce projected light 338 into the eyes302, 304 and facilitate beam shaping, while also allowing fortransmission of at least some light from the local environment. Thewavefront of the projected light beam 338 may be bent or focused tocoincide with a desired focal distance of the projected light. Asillustrated, two wide-field of view machine vision cameras 316 (alsoreferred to as world cameras) may be coupled to the housing 230 to imagethe environment around the user. These cameras 316 may be dual capturevisible light/non-visible (e.g., infrared) light cameras. The cameras316 may be part of the outward-facing imaging system 464 shown in FIG.4. Image acquired by the world cameras 316 may be processed by the poseprocessor 336. For example, the pose processor 336 may implement one ormore object recognizers 708 (e.g., shown in FIG. 7) to identify a poseof a user or another person in the user's environment or to identify aphysical object in the user's environment.

With continued reference to FIG. 3, a pair of light projector modules(e.g., scanned-laser shaped-wavefront (e.g., for depth) light projectormodules) with display mirrors and optics configured to project light 338into the eyes 302, 304 are shown. The depicted view also shows twominiature infrared cameras 324 paired with infrared light sources 326(such as light emitting diodes “LED”s), which are configured to be ableto track the eyes 302, 304 of the user to support rendering and userinput. The cameras 324 may be part of the inward-facing imaging system462 shown in FIG. 4. The wearable system 200 may further feature asensor assembly 339, which may comprise X, Y, and Z axis accelerometercapability as well as a magnetic compass and X, Y, and Z axis gyrocapability, preferably providing data at a relatively high frequency,such as 200 Hz. The sensor assembly 339 may be part of the IMU describedwith reference to FIG. 2A The depicted system 200 may also comprise ahead pose processor 336, such as an ASIC (application specificintegrated circuit), FPGA (field programmable gate array), or ARMprocessor (advanced reduced-instruction-set machine), which may beconfigured to calculate real or near-real time user head pose from widefield of view image information output from the capture devices 316. Thehead pose processor 336 may be a hardware processor and may beimplemented as part of the local processing and data module 260 shown inFIG. 2A.

The wearable system may also include one or more depth sensors 234. Thedepth sensor 234 may be configured to measure the distance between anobject in an environment to a wearable device. The depth sensor 234 mayinclude a laser scanner (e.g., a lidar), an ultrasonic depth sensor, ora depth sensing camera. In certain implementations, where the cameras316 have depth sensing ability, the cameras 316 may also be consideredas depth sensors 234.

Also shown is a processor 332 configured to execute digital or analogprocessing to derive pose from the gyro, compass, or accelerometer datafrom the sensor assembly 339. The processor 332 may be part of the localprocessing and data module 260 shown in FIG. 2. The wearable system 200as shown in FIG. 3 may also include a position system such as, e.g., aGPS 337 (global positioning system) to assist with pose and positioninganalyses. In addition, the GPS may further provide remotely-based (e.g.,cloud-based) information about the user's environment. This informationmay be used for recognizing objects or information in user'senvironment.

The wearable system may combine data acquired by the GPS 337 and aremote computing system (such as, e.g., the remote processing module270, another user's ARD, etc.) which may provide more information aboutthe user's environment. As one example, the wearable system maydetermine the user's location based on GPS data and retrieve a world map(e.g., by communicating with a remote processing module 270) includingvirtual objects associated with the user's location. As another example,the wearable system 200 may monitor the environment using the worldcameras 316 (which may be part of the outward-facing imaging system 464shown in FIG. 4). Based on the images acquired by the world cameras 316,the wearable system 200 may detect objects in the environment (e.g., byusing one or more object recognizers 708 shown in FIG. 7). The wearablesystem may further use data acquired by the GPS 337 to interpret thecharacters.

The wearable system 200 may also comprise a rendering engine 334 whichmay be configured to provide rendering information that is local to theuser to facilitate operation of the scanners and imaging into the eyesof the user, for the user's view of the world. The rendering engine 334may be implemented by a hardware processor (such as, e.g., a centralprocessing unit or a graphics processing unit). In some embodiments, therendering engine is part of the local processing and data module 260.The rendering engine 334 may be communicatively coupled (e.g., via wiredor wireless links) to other components of the wearable system 200. Forexample, the rendering engine 334, may be coupled to the eye cameras 324via communication link 274, and be coupled to a projecting subsystem 318(which may project light into user's eyes 302, 304 via a scanned laserarrangement in a manner similar to a retinal scanning display) via thecommunication link 272. The rendering engine 334 may also be incommunication with other processing units such as, e.g., the sensor poseprocessor 332 and the image pose processor 336 via links 276 and 294respectively.

The cameras 324 (e.g., mini infrared cameras) may be utilized to trackthe eye pose to support rendering and user input. Some example eye posesmay include where the user is looking or at what depth he or she isfocusing (which may be estimated with eye vergence). The GPS 337, gyros,compass, and accelerometers 339 may be utilized to provide coarse orfast pose estimates. One or more of the cameras 316 may acquire imagesand pose, which in conjunction with data from an associated cloudcomputing resource, may be utilized to map the local environment andshare user views with others.

The example components depicted in FIG. 3 are for illustration purposesonly. Multiple sensors and other functional modules are shown togetherfor ease of illustration and description. Some embodiments may includeonly one or a subset of these sensors or modules. Further, the locationsof these components are not limited to the positions depicted in FIG. 3.Some components may be mounted to or housed within other components,such as a belt-mounted component, a hand-held component, or a helmetcomponent. As one example, the image pose processor 336, sensor poseprocessor 332, and rendering engine 334 may be positioned in a beltpackand configured to communicate with other components of the wearablesystem via wireless communication, such as ultra-wideband, Wi-Fi,Bluetooth, etc., or via wired communication. The depicted housing 230preferably is head-mountable and wearable by the user. However, somecomponents of the wearable system 200 may be worn to other portions ofthe user's body. For example, the speaker 240 may be inserted into theears of a user to provide sound to the user.

Regarding the projection of light 338 into the eyes 302, 304 of theuser, in some embodiment, the cameras 324 may be utilized to measurewhere the centers of a user's eyes are geometrically verged to, which,in general, coincides with a position of focus, or “depth of focus”, ofthe eyes. A 3-dimensional surface of all points the eyes verge to may bereferred to as the “horopter”. The focal distance may take on a finitenumber of depths, or may be infinitely varying. Light projected from thevergence distance appears to be focused to the subject eye 302, 304,while light in front of or behind the vergence distance is blurred.Examples of wearable devices and other display systems of the presentdisclosure are also described in U.S. Patent Publication No.2016/0270656, which is incorporated by reference herein in its entirety.

The human visual system is complicated and providing a realisticperception of depth is challenging. Viewers of an object may perceivethe object as being three-dimensional due to a combination of vergenceand accommodation. Vergence movements (e.g., rolling movements of thepupils toward or away from each other to converge the lines of sight ofthe eyes to fixate upon an object) of the two eyes relative to eachother are closely associated with focusing (or “accommodation”) of thelenses of the eyes. Under normal conditions, changing the focus of thelenses of the eyes, or accommodating the eyes, to change focus from oneobject to another object at a different distance will automaticallycause a matching change in vergence to the same distance, under arelationship known as the “accommodation-vergence reflex.” Likewise, achange in vergence will trigger a matching change in accommodation,under normal conditions. Display systems that provide a better matchbetween accommodation and vergence may form more realistic andcomfortable simulations of three-dimensional imagery.

Further spatially coherent light with a beam diameter of less than about0.7 millimeters may be correctly resolved by the human eye regardless ofwhere the eye focuses. Thus, to create an illusion of proper focaldepth, the eye vergence may be tracked with the cameras 324, and therendering engine 334 and projection subsystem 318 may be utilized torender all objects on or close to the horopter in focus, and all otherobjects at varying degrees of defocus (e.g., using intentionally-createdblurring). Preferably, the system 220 renders to the user at a framerate of about 60 frames per second or greater. As described above,preferably, the cameras 324 may be utilized for eye tracking, andsoftware may be configured to pick up not only vergence geometry butalso focus location cues to serve as user inputs. Preferably, such adisplay system is configured with brightness and contrast suitable forday or night use.

In some embodiments, the display system preferably has latency of lessthan about 20 milliseconds for visual object alignment, less than about0.1 degree of angular alignment, and about 1 arc minute of resolution,which, without being limited by theory, is believed to be approximatelythe limit of the human eye. The display system 220 may be integratedwith a localization system, which may involve GPS elements, opticaltracking, compass, accelerometers, or other data sources, to assist withposition and pose determination; localization information may beutilized to facilitate accurate rendering in the user's view of thepertinent world (e.g., such information would facilitate the glasses toknow where they are with respect to the real world).

In some embodiments, the wearable system 200 is configured to displayone or more virtual images based on the accommodation of the user'seyes. Unlike prior 3D display approaches that force the user to focuswhere the images are being projected, in some embodiments, the wearablesystem is configured to automatically vary the focus of projectedvirtual content to allow for a more comfortable viewing of one or moreimages presented to the user. For example, if the user's eyes have acurrent focus of 1 m, the image may be projected to coincide with theuser's focus. If the user shifts focus to 3 m, the image is projected tocoincide with the new focus. Thus, rather than forcing the user to apredetermined focus, the wearable system 200 of some embodiments allowsthe user's eye to a function in a more natural manner.

Such a wearable system 200 may eliminate or reduce the incidences of eyestrain, headaches, and other physiological symptoms typically observedwith respect to virtual reality devices. To achieve this, variousembodiments of the wearable system 200 are configured to project virtualimages at varying focal distances, through one or more variable focuselements (VFEs). In one or more embodiments, 3D perception may beachieved through a multi-plane focus system that projects images atfixed focal planes away from the user. Other embodiments employ variableplane focus, wherein the focal plane is moved back and forth in thez-direction to coincide with the user's present state of focus.

In both the multi-plane focus systems and variable plane focus systems,wearable system 200 may employ eye tracking to determine a vergence ofthe user's eyes, determine the user's current focus, and project thevirtual image at the determined focus. In other embodiments, wearablesystem 200 comprises a light modulator that variably projects, through afiber scanner, or other light generating source, light beams of varyingfocus in a raster pattern across the retina. Thus, the ability of thedisplay of the wearable system 200 to project images at varying focaldistances not only eases accommodation for the user to view objects in3D, but may also be used to compensate for user ocular anomalies, asfurther described in U.S. Patent Publication No. 2016/0270656, which isincorporated by reference herein in its entirety. In some otherembodiments, a spatial light modulator may project the images to theuser through various optical components. For example, as describedfurther below, the spatial light modulator may project the images ontoone or more waveguides, which then transmit the images to the user.

Waveguide Stack Assembly

FIG. 4 illustrates an example of a waveguide stack for outputting imageinformation to a user. A wearable system 400 includes a stack ofwaveguides, or stacked waveguide assembly 480 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 432 b, 434 b, 436 b, 438 b, 4400 b. In some embodiments,the wearable system 400 may correspond to wearable system 200 of FIG. 2,with FIG. 4 schematically showing some parts of that wearable system 200in greater detail. For example, in some embodiments, the waveguideassembly 480 may be integrated into the display 220 of FIG. 2.

With continued reference to FIG. 4, the waveguide assembly 480 may alsoinclude a plurality of features 458, 456, 454, 452 between thewaveguides. In some embodiments, the features 458, 456, 454, 452 may belenses. In other embodiments, the features 458, 456, 454, 452 may not belenses. Rather, they may simply be spacers (e.g., cladding layers orstructures for forming air gaps).

The waveguides 432 b, 434 b, 436 b, 438 b, 440 b or the plurality oflenses 458, 456, 454, 452 may be configured to send image information tothe eye with various levels of wavefront curvature or light raydivergence. Each waveguide level may be associated with a particulardepth plane and may be configured to output image informationcorresponding to that depth plane. Image injection devices 420, 422,424, 426, 428 may be utilized to inject image information into thewaveguides 440 b, 438 b, 436 b, 434 b, 432 b, each of which may beconfigured to distribute incoming light across each respectivewaveguide, for output toward the eye 410. Light exits an output surfaceof the image injection devices 420, 422, 424, 426, 428 and is injectedinto a corresponding input edge of the waveguides 440 b, 438 b, 436 b,434 b, 432 b. In some embodiments, a single beam of light (e.g., acollimated beam) may be injected into each waveguide to output an entirefield of cloned collimated beams that are directed toward the eye 410 atparticular angles (and amounts of divergence) corresponding to the depthplane associated with a particular waveguide.

In some embodiments, the image injection devices 420, 422, 424, 426, 428are discrete displays that each produce image information for injectioninto a corresponding waveguide 440 b, 438 b, 436 b, 434 b, 432 b,respectively. In some other embodiments, the image injection devices420, 422, 424, 426, 428 are the output ends of a single multiplexeddisplay which may, e.g., pipe image information via one or more opticalconduits (such as fiber optic cables) to each of the image injectiondevices 420, 422, 424, 426, 428.

A controller 460 controls the operation of the stacked waveguideassembly 480 and the image injection devices 420, 422, 424, 426, 428.The controller 460 includes programming (e.g., instructions in anon-transitory computer-readable medium) that regulates the timing andprovision of image information to the waveguides 440 b, 438 b, 436 b,434 b, 432 b. In some embodiments, the controller 460 may be a singleintegral device, or a distributed system connected by wired or wirelesscommunication channels. The controller 460 may be part of the processingmodules 260 or 270 (illustrated in FIG. 2) in some embodiments.

The waveguides 440 b, 438 b, 436 b, 434 b, 432 b may be configured topropagate light within each respective waveguide by total internalreflection (TIR). The waveguides 440 b, 438 b, 436 b, 434 b, 432 b mayeach be planar or have another shape (e.g., curved), with major top andbottom surfaces and edges extending between those major top and bottomsurfaces. In the illustrated configuration, the waveguides 440 b, 438 b,436 b, 434 b, 432 b may each include light extracting optical elements440 a, 438 a, 436 a, 434 a, 432 a that are configured to extract lightout of a waveguide by redirecting the light, propagating within eachrespective waveguide, out of the waveguide to output image informationto the eye 410. Extracted light may also be referred to as outcoupledlight, and light extracting optical elements may also be referred to asoutcoupling optical elements. An extracted beam of light is outputted bythe waveguide at locations at which the light propagating in thewaveguide strikes a light redirecting element. The light extractingoptical elements (440 a, 438 a, 436 a, 434 a, 432 a) may, for example,be reflective or diffractive optical features. While illustrateddisposed at the bottom major surfaces of the waveguides 440 b, 438 b,436 b, 434 b, 432 b for ease of description and drawing clarity, in someembodiments, the light extracting optical elements 440 a, 438 a, 436 a,434 a, 432 a may be disposed at the top or bottom major surfaces, or maybe disposed directly in the volume of the waveguides 440 b, 438 b, 436b, 434 b, 432 b. In some embodiments, the light extracting opticalelements 440 a, 438 a, 436 a, 434 a, 432 a may be formed in a layer ofmaterial that is attached to a transparent substrate to form thewaveguides 440 b, 438 b, 436 b, 434 b, 432 b. In some other embodiments,the waveguides 440 b, 438 b, 436 b, 434 b, 432 b may be a monolithicpiece of material and the light extracting optical elements 440 a, 438a, 436 a, 434 a, 432 a may be formed on a surface or in the interior ofthat piece of material.

With continued reference to FIG. 4, as discussed herein, each waveguide440 b, 438 b, 436 b, 434 b, 432 b is configured to output light to forman image corresponding to a particular depth plane. For example, thewaveguide 432 b nearest the eye may be configured to deliver collimatedlight, as injected into such waveguide 432 b, to the eye 410. Thecollimated light may be representative of the optical infinity focalplane. The next waveguide up 434 b may be configured to send outcollimated light which passes through the first lens 452 (e.g., anegative lens) before it may reach the eye 410. First lens 452 may beconfigured to create a slight convex wavefront curvature so that theeye/brain interprets light coming from that next waveguide up 434 b ascoming from a first focal plane closer inward toward the eye 410 fromoptical infinity. Similarly, the third up waveguide 436 b passes itsoutput light through both the first lens 452 and second lens 454 beforereaching the eye 410. The combined optical power of the first and secondlenses 452 and 454 may be configured to create another incrementalamount of wavefront curvature so that the eye/brain interprets lightcoming from the third waveguide 436 b as coming from a second focalplane that is even closer inward toward the person from optical infinitythan was light from the next waveguide up 434 b.

The other waveguide layers (e.g., waveguides 438 b, 440 b) and lenses(e.g., lenses 456, 458) are similarly configured, with the highestwaveguide 440 b in the stack sending its output through all of thelenses between it and the eye for an aggregate focal powerrepresentative of the closest focal plane to the person. To compensatefor the stack of lenses 458, 456, 454, 452 when viewing/interpretinglight coming from the world 470 on the other side of the stackedwaveguide assembly 480, a compensating lens layer 430 may be disposed atthe top of the stack to compensate for the aggregate power of the lensstack 458, 456, 454, 452 below. (Compensating lens layer 430 and thestacked waveguide assembly 480 as a whole may be configured such thatlight coming from the world 470 is conveyed to the eye 410 atsubstantially the same level of divergence (or collimation) as the lighthad when it was initially received by the stacked waveguide assembly480.) Such a configuration provides as many perceived focal planes asthere are available waveguide/lens pairings. Both the light extractingoptical elements of the waveguides and the focusing aspects of thelenses may be static (e.g., not dynamic or electro-active). In somealternative embodiments, either or both may be dynamic usingelectro-active features.

With continued reference to FIG. 4, the light extracting opticalelements 440 a, 438 a, 436 a, 434 a, 432 a may be configured to bothredirect light out of their respective waveguides and to output thislight with the appropriate amount of divergence or collimation for aparticular depth plane associated with the waveguide. As a result,waveguides having different associated depth planes may have differentconfigurations of light extracting optical elements, which output lightwith a different amount of divergence depending on the associated depthplane. In some embodiments, as discussed herein, the light extractingoptical elements 440 a, 438 a, 436 a, 434 a, 432 a may be volumetric orsurface features, which may be configured to output light at specificangles. For example, the light extracting optical elements 440 a, 438 a,436 a, 434 a, 432 a may be volume holograms, surface holograms, and/ordiffraction gratings. Light extracting optical elements, such asdiffraction gratings, are described in U.S. Patent Publication No.2015/0178939, published Jun. 25, 2015, which is incorporated byreference herein in its entirety.

In some embodiments, the light extracting optical elements 440 a, 438 a,436 a, 434 a, 432 a are diffractive features that form a diffractionpattern, or “diffractive optical element” (also referred to herein as a“DOE”). Preferably, the DOE has a relatively low diffraction efficiencyso that only a portion of the light of the beam is deflected away towardthe eye 410 with each intersection of the DOE, while the rest continuesto move through a waveguide via total internal reflection. The lightcarrying the image information may thus be divided into a number ofrelated exit beams that exit the waveguide at a multiplicity oflocations and the result is a fairly uniform pattern of exit emissiontoward the eye 304 for this particular collimated beam bouncing aroundwithin a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”state in which they actively diffract, and “off” state in which they donot significantly diffract. For instance, a switchable DOE may comprisea layer of polymer dispersed liquid crystal, in which microdropletscomprise a diffraction pattern in a host medium, and the refractiveindex of the microdroplets may be switched to substantially match therefractive index of the host material (in which case the pattern doesnot appreciably diffract incident light) or the microdroplet may beswitched to an index that does not match that of the host medium (inwhich case the pattern actively diffracts incident light).

In some embodiments, the number and distribution of depth planes ordepth of field may be varied dynamically based on the pupil sizes ororientations of the eyes of the viewer. Depth of field may changeinversely with a viewer's pupil size. As a result, as the sizes of thepupils of the viewer's eyes decrease, the depth of field increases suchthat one plane that is not discernible because the location of thatplane is beyond the depth of focus of the eye may become discernible andappear more in focus with reduction of pupil size and commensurate withthe increase in depth of field. Likewise, the number of spaced apartdepth planes used to present different images to the viewer may bedecreased with the decreased pupil size. For example, a viewer may notbe able to clearly perceive the details of both a first depth plane anda second depth plane at one pupil size without adjusting theaccommodation of the eye away from one depth plane and to the otherdepth plane. These two depth planes may, however, be sufficiently infocus at the same time to the user at another pupil size withoutchanging accommodation.

In some embodiments, the display system may vary the number ofwaveguides receiving image information based upon determinations ofpupil size or orientation, or upon receiving electrical signalsindicative of particular pupil size or orientation. For example, if theuser's eyes are unable to distinguish between two depth planesassociated with two waveguides, then the controller 460 (which may be anembodiment of the local processing and data module 260) may beconfigured or programmed to cease providing image information to one ofthese waveguides. Advantageously, this may reduce the processing burdenon the system, thereby increasing the responsiveness of the system. Inembodiments in which the DOEs for a waveguide are switchable between theon and off states, the DOEs may be switched to the off state when thewaveguide does receive image information.

In some embodiments, it may be desirable to have an exit beam meet thecondition of having a diameter that is less than the diameter of the eyeof a viewer. However, meeting this condition may be challenging in viewof the variability in size of the viewer's pupils. In some embodiments,this condition is met over a wide range of pupil sizes by varying thesize of the exit beam in response to determinations of the size of theviewer's pupil. For example, as the pupil size decreases, the size ofthe exit beam may also decrease. In some embodiments, the exit beam sizemay be varied using a variable aperture.

The wearable system 400 may include an outward-facing imaging system 464(e.g., a digital camera) that images a portion of the world 470. Thisportion of the world 470 may be referred to as the field of view (FOV)of a world camera and the imaging system 464 is sometimes referred to asan FOV camera. The FOV of the world camera may or may not be the same asthe FOV of a viewer 210 which encompasses a portion of the world 470 theviewer 210 perceives at a given time. For example, in some situations,the FOV of the world camera may be larger than the viewer 210 of theviewer 210 of the wearable system 400. The entire region available forviewing or imaging by a viewer may be referred to as the field of regard(FOR). The FOR may include 4π steradians of solid angle surrounding thewearable system 400 because the wearer may move his body, head, or eyesto perceive substantially any direction in space. In other contexts, thewearer's movements may be more constricted, and accordingly the wearer'sFOR may subtend a smaller solid angle. Images obtained from theoutward-facing imaging system 464 may be used to track gestures made bythe user (e.g., hand or finger gestures), detect objects in the world470 in front of the user, and so forth.

The wearable system 400 may include an audio sensor 232, e.g., amicrophone, to capture ambient sound. As described above, in someembodiments, one or more other audio sensors may be positioned toprovide stereo sound reception useful to the determination of locationof a speech source. The audio sensor 232 may comprise a directionalmicrophone, as another example, which may also provide such usefuldirectional information as to where the audio source is located. Thewearable system 400 may use information from both the outward-facingimaging system 464 and the audio sensor 230 in locating a source ofspeech, or to determine an active speaker at a particular moment intime, etc. For example, the wearable system 400 may use the voicerecognition alone or in combination with a reflected image of thespeaker (e.g., as seen in a mirror) to determine the identity of thespeaker. As another example, the wearable system 400 may determine aposition of the speaker in an environment based on sound acquired fromdirectional microphones. The wearable system 400 may parse the soundcoming from the speaker's position with speech recognition algorithms todetermine the content of the speech and use voice recognition techniquesto determine the identity (e.g., name or other demographic information)of the speaker.

The wearable system 400 may also include an inward-facing imaging system466 (e.g., a digital camera), which observes the movements of the user,such as the eye movements and the facial movements. The inward-facingimaging system 466 may be used to capture images of the eye 410 todetermine the size and/or orientation of the pupil of the eye 304. Theinward-facing imaging system 466 may be used to obtain images for use indetermining the direction the user is looking (e.g., eye pose) or forbiometric identification of the user (e.g., via iris identification). Insome embodiments, at least one camera may be utilized for each eye, toseparately determine the pupil size or eye pose of each eyeindependently, thereby allowing the presentation of image information toeach eye to be dynamically tailored to that eye. In some otherembodiments, the pupil diameter or orientation of only a single eye 410(e.g., using only a single camera per pair of eyes) is determined andassumed to be similar for both eyes of the user. The images obtained bythe inward-facing imaging system 466 may be analyzed to determine theuser's eye pose or mood, which may be used by the wearable system 400 todecide which audio or visual content should be presented to the user.The wearable system 400 may also determine head pose (e.g., headposition or head orientation) using sensors such as IMUs,accelerometers, gyroscopes, etc.

The wearable system 400 may include a user input device 466 by which theuser may input commands to the controller 460 to interact with thewearable system 400. For example, the user input device 466 may includea trackpad, a touchscreen, a joystick, a multiple degree-of-freedom(DOF) controller, a capacitive sensing device, a game controller, akeyboard, a mouse, a directional pad (D-pad), a wand, a haptic device, atotem (e.g., functioning as a virtual user input device), and so forth.A multi-DOF controller may sense user input in some or all possibletranslations (e.g., left/right, forward/backward, or up/down) orrotations (e.g., yaw, pitch, or roll) of the controller. A multi-DOFcontroller which supports the translation movements may be referred toas a 3DOF while a multi-DOF controller which supports the translationsand rotations may be referred to as κDOF. In some cases, the user mayuse a finger (e.g., a thumb) to press or swipe on a touch-sensitiveinput device to provide input to the wearable system 400 (e.g., toprovide user input to a user interface provided by the wearable system400). The user input device 466 may be held by the user's hand duringthe use of the wearable system 400. The user input device 466 may be inwired or wireless communication with the wearable system 400.

Other Components of the Wearable System

In many implementations, the wearable system may include othercomponents in addition or in alternative to the components of thewearable system described above. The wearable system may, for example,include one or more haptic devices or components. The haptic devices orcomponents may be operable to provide a tactile sensation to a user. Forexample, the haptic devices or components may provide a tactilesensation of pressure or texture when touching virtual content (e.g.,virtual objects, virtual tools, other virtual constructs). The tactilesensation may replicate a feel of a physical object which a virtualobject represents, or may replicate a feel of an imagined object orcharacter (e.g., a dragon) which the virtual content represents. In someimplementations, haptic devices or components may be worn by the user(e.g., a user wearable glove). In some implementations, haptic devicesor components may be held by the user.

The wearable system may, for example, include one or more physicalobjects which are manipulable by the user to allow input or interactionwith the wearable system. These physical objects may be referred toherein as totems. Some totems may take the form of inanimate objects,such as for example, a piece of metal or plastic, a wall, a surface oftable. In certain implementations, the totems may not actually have anyphysical input structures (e.g., keys, triggers, joystick, trackball,rocker switch). Instead, the totem may simply provide a physicalsurface, and the wearable system may render a user interface so as toappear to a user to be on one or more surfaces of the totem. Forexample, the wearable system may render an image of a computer keyboardand trackpad to appear to reside on one or more surfaces of a totem. Forexample, the wearable system may render a virtual computer keyboard andvirtual trackpad to appear on a surface of a thin rectangular plate ofaluminum which serves as a totem. The rectangular plate does not itselfhave any physical keys or trackpad or sensors. However, the wearablesystem may detect user manipulation or interaction or touches with therectangular plate as selections or inputs made via the virtual keyboardor virtual trackpad. The user input device 466 (shown in FIG. 4) may bean embodiment of a totem, which may include a trackpad, a touchpad, atrigger, a joystick, a trackball, a rocker or virtual switch, a mouse, akeyboard, a multi-degree-of-freedom controller, or another physicalinput device. A user may use the totem, alone or in combination withposes, to interact with the wearable system or other users.

Examples of haptic devices and totems usable with the wearable devices,HMD, and display systems of the present disclosure are described in U.S.Patent Publication No. 2015/0016777, which is incorporated by referenceherein in its entirety.

Example of an Eye Image

FIG. 5 illustrates an image of an eye 500 with eyelids 504, sclera 508(the “white” of the eye), iris 512, and pupil 516. Curve 516 a shows thepupillary boundary between the pupil 516 and the iris 512, and curve 512a shows the limbic boundary between the iris 512 and the sclera 508. Theeyelids 504 include an upper eyelid 504 a and a lower eyelid 504 b. Theeye 500 is illustrated in a natural resting pose (e.g., in which theuser's face and gaze are both oriented as they would be toward a distantobject directly ahead of the user). The natural resting pose of the eye500 may be indicated by a natural resting direction 520, which is adirection orthogonal to the surface of the eye 500 when in the naturalresting pose (e.g., directly out of the plane for the eye 500 shown inFIG. 5) and in this example, centered within the pupil 516.

As the eye 500 moves to look toward different objects, the eye pose willchange relative to the natural resting direction 520. The current eyepose may be determined with reference to an eye pose direction 524,which is a direction orthogonal to the surface of the eye (and centeredin within the pupil 516) but oriented toward the object at which the eyeis currently directed. With reference to an example coordinate systemshown in FIG. 5, the pose of the eye 500 may be expressed as two angularparameters indicating an azimuthal deflection and a zenithal deflectionof the eye pose direction 524 of the eye, both relative to the naturalresting direction 520 of the eye. For purposes of illustration, theseangular parameters may be represented as θ (azimuthal deflection,determined from a fiducial azimuth) and ϕ (zenithal deflection,sometimes also referred to as a polar deflection). In someimplementations, angular roll of the eye around the eye pose direction524 may be included in the determination of eye pose, and angular rollmay be included in the following analysis. In other implementations,other techniques for determining the eye pose may be used, for example,a pitch, yaw, and optionally roll system.

An eye image may be obtained from a video using any appropriate process,for example, using a video processing algorithm that may extract animage from one or more sequential frames. The pose of the eye may bedetermined from the eye image using a variety of eye-trackingtechniques. For example, an eye pose may be determined by consideringthe lensing effects of the cornea on light sources that are provided.Any suitable eye tracking technique may be used for determining eye posein the eyelid shape estimation techniques described herein.

Example of an Eye Tracking System

FIG. 6 illustrates a schematic diagram of a wearable, or a head-mounted,display system 600 that includes an eye tracking system. Thehead-mounted display system 600 may, in at least some embodiments,include components located in a head-mounted unit 602 and componentslocated in a non-head-mounted unit 604. Non-head mounted unit 604 maybe, as examples, a belt-mounted component, a hand-held component, acomponent in a backpack, a remote component, etc. Incorporating some ofthe components of the head-mounted display system 600 innon-head-mounted unit 604 may help to reduce the size, weight,complexity, and cost of the head-mounted unit 602. In someimplementations, some or all of the functionality described as beingperformed by one or more components of head-mounted unit 602 and/ornon-head mounted 604 may be provided by way of one or more componentsincluded elsewhere in the head-mounted display system 600. For example,some or all of the functionality described below in association with aCPU 612 of head-mounted unit 602 may be provided by way of a CPU 616 ofnon-head mounted unit 604, and vice versa. In some examples, some or allof such functionality may be provided by way of peripheral devices ofhead-mounted display system 600. Furthermore, in some implementations,some or all of such functionality may be provided by way of one or morecloud computing devices or other remotely-located computing devices in amanner similar to that which has been described above with reference toFIG. 2.

As shown in FIG. 6, head-mounted display system 600 may include an eyetracking system including a camera 324 that captures images of a user'seye 610. If desired, the eye tracking system may also include lightsources 326 a and 326 b (such as light emitting diodes “LED”s). Thelight sources 326 a and 326 b may generate glints (i.e., reflections offof the user's eyes that appear in images of the eye captured by camera324). The positions of the light sources 326 a and 326 b relative to thecamera 324 may be known and, as a consequence, the positions of theglints within images captured by camera 324 may be used in tracking theuser's eyes (as will be discussed in more detail below in connectionwith FIGS. 7-11). In at least one embodiment, there may be one lightsource 326 and one camera 324 associated with a single one of the user'seyes 610. In another embodiment, there may be one light source 326 andone camera 324 associated with each of a user's eyes. 610. In yet otherembodiments, there may be one or more cameras 324 and one or more lightsources 326 associated with one or each of a user's eyes 610. As aspecific example, there may be two light sources 326 a and 326 b and oneor more cameras 324 associated with each of a user's eyes 610. Asanother example, there may be three or more light sources such as lightsources 326 a and 326 b and one or more cameras 324 associated with eachof a user's eyes 610.

Eye tracking module 614 may receive images from eye-tracking camera(s)324 and may analyze the images to extract various pieces of information.As examples, the eye tracking module 614 may detect the user's eyeposes, a three-dimensional position of the user's eye relative to theeye-tracking camera 324 (and to the head-mounted unit 602), thedirection one or both of the user's eyes 610 are focused on, the user'svergence depth (i.e., the depth from the user at which the user isfocusing on), the positions of the user's pupils, the positions of theuser's cornea and cornea sphere, the center of rotation of each of theuser's eyes, and the center of perspective of each of the user's eyes.The eye tracking module 614 may extract such information usingtechniques described below in connection with FIGS. 7-11. As shown inFIG. 6, eye tracking module 614 may be a software module implementedusing a CPU 612 in a head-mounted unit 602.

Data from eye tracking module 614 may be provided to other components inthe wearable system. As example, such data may be transmitted tocomponents in a non-head-mounted unit 604 such as CPU 616 includingsoftware modules for a light-field render controller 618 and aregistration observer 620, which may be configured to evaluate whetherthe display of the head-mounted display system 600 is properlyregistered with the eyes of the user.

Render controller 618 may use information from eye tracking module 614to adjust images displayed to the user by render engine 622 (e.g., arender engine that may be a software module in GPU 621 and that mayprovide images to display 220). As an example, the render controller 618may adjust images displayed to the user based on the user's center ofrotation or center of perspective. In particular, the render controller618 may use information on the user's center of perspective to simulatea render camera (i.e., to simulate collecting images from the user'sperspective) and may adjust images displayed to the user based on thesimulated render camera.

A “render camera,” which is sometimes also referred to as a “pinholeperspective camera” (or simply “perspective camera”) or “virtual pinholecamera” (or simply “virtual camera”), is a simulated camera for use inrendering virtual image content possibly from a database of objects in avirtual world. The objects may have locations and orientations relativeto the user or wearer and possibly relative to real objects in theenvironment surrounding the user or wearer. In other words, the rendercamera may represent a perspective within render space from which theuser or wearer is to view 3D virtual contents of the render space (e.g.,virtual objects). The render camera may be managed by a render engine torender virtual images based on the database of virtual objects to bepresented to the eye. The virtual images may be rendered as if takenfrom the perspective the user or wearer. For example, the virtual imagesmay be rendered as if captured by a pinhole camera (corresponding to the“render camera”) having a specific set of intrinsic parameters (e.g.,focal length, camera pixel size, principal point coordinates,skew/distortion parameters, etc.), and a specific set of extrinsicparameters (e.g., translational components and rotational componentsrelative to the virtual world). The virtual images are taken from theperspective of such a camera having the position and orientation of therender camera (e.g., extrinsic parameters of the render camera). Itfollows that the system may define and/or adjust intrinsic and extrinsicrender camera parameters. For example, the system may define aparticular set of extrinsic render camera parameters such that virtualimages may be rendered as if captured from the perspective of a camerahaving a specific location with respect to the user's or wearer's eye soas to provide images that appear to be from the perspective of the useror wearer. The system may later dynamically adjust extrinsic rendercamera parameters on-the-fly so as to maintain registration with thespecific location. Similarly, intrinsic render camera parameters may bedefined and dynamically adjusted over time. In some implementations, theimages are rendered as if captured from the perspective of a camerahaving an aperture (e.g., pinhole) at a specific location with respectto the user's or wearer's eye (such as the center of perspective orcenter of rotation, or elsewhere).

In some embodiments, the system may create or dynamically repositionand/or reorient one render camera for the user's left eye, and anotherrender camera for the user's right eye, as the user's eyes arephysically separated from one another and thus consistently positionedat different locations. It follows that, in at least someimplementations, virtual content rendered from the perspective of arender camera associated with the viewer's left eye may be presented tothe user through an eyepiece on the left side of a head-mounted display(e.g., head-mounted unit 602), and that virtual content rendered fromthe perspective of a render camera associated with the user's right eyemay be presented to the user through an eyepiece on the right side ofsuch a head-mounted display. Further details discussing the creation,adjustment, and use of render cameras in rendering processes areprovided in U.S. patent application Ser. No. 15/274,823, entitled“METHODS AND SYSTEMS FOR DETECTING AND COMBINING STRUCTURAL FEATURES IN3D RECONSTRUCTION,” which is expressly incorporated herein by referencein its entirety for all purposes.

In some examples, one or more modules (or components) of the system 600(e.g., light-field render controller 618, render engine 622, etc.) maydetermine the position and orientation of the render camera withinrender space based on the position and orientation of the user's headand eyes (e.g., as determined based on head pose and eye tracking data,respectively). That is, the system 600 may effectively map the positionand orientation of the user's head and eyes to particular locations andangular positions within a 3D virtual environment, place and orientrender cameras at the particular locations and angular positions withinthe 3D virtual environment, and render virtual content for the user asit would be captured by the render camera. Further details discussingreal world to virtual world mapping processes are provided in U.S.patent application Ser. No. 15/296,869, entitled “SELECTING VIRTUALOBJECTS IN A THREE-DIMENSIONAL SPACE,” which is expressly incorporatedherein by reference in its entirety for all purposes. As an example, therender controller 618 may adjust the depths at which images aredisplayed by selecting which depth plane (or depth planes) are utilizedat any given time to display the images. In some implementations, such adepth plane switch may be carried out through an adjustment of one ormore intrinsic render camera parameters.

Registration observer 620 may use information from eye tracking module614 to identify whether the head-mounted unit 602 is properly positionedon a user's head. As an example, the eye tracking module 614 may provideeye location information, such as the positions of the centers ofrotation of the user's eyes, indicative of the three-dimensionalposition of the user's eyes relative to camera 324 and head-mounted unit602 and the eye tracking module 614 may use the location information todetermine if display 220 is properly aligned in the user's field ofview, or if the head-mounted unit 602 (or headset) has slipped or isotherwise misaligned with the user's eyes. As examples, the registrationobserver 620 may be able to determine if the head-mounted unit 602 hasslipped down the user's nose bridge, thus moving display 220 away anddown from the user's eyes (which may be undesirable), if thehead-mounted unit 602 has been moved up the user's nose bridge, thusmoving display 220 closer and up from the user's eyes, if thehead-mounted unit 602 has been shifted left or right relative the user'snose bridge, if the head-mounted unit 602 has been lifted above theuser's nose bridge, or if the head-mounted unit 602 has been moved inthese or other ways away from a desired position or range of positions.In general, registration observer 620 may be able to determine ifhead-mounted unit 602, in general, and displays 220, in particular, areproperly positioned in front of the user's eyes. In other words, theregistration observer 620 may determine if a left display in displaysystem 220 is appropriately aligned with the user's left eye and a rightdisplay in display system 220 is appropriately aligned with the user'sright eye. The registration observer 620 may determine if thehead-mounted unit 602 is properly positioned by determining if thehead-mounted unit 602 is positioned and oriented within a desired rangeof positions and/or orientations relative to the user's eyes.

In at least some embodiments, registration observer 620 may generateuser feedback in the form of alerts, messages, or other content. Suchfeedback may be provided to the user to inform the user of anymisalignment of the head-mounted unit 602, along with optional feedbackon how to correct the misalignment (such as a suggestion to adjust thehead-mounted unit 602 in a particular manner).

Example registration observation and feedback techniques, which may beutilized by registration observer 620, are described in U.S. patentapplication Ser. No. 15/717,747, filed Sep. 27, 2017, which isincorporated by reference herein in its entirety.

Example of an Eye Tracking Module

A detailed block diagram of an example eye tracking module 614 is shownin FIG. 7A. As shown in FIG. 7A, eye tracking module 614 may include avariety of different submodules, may provide a variety of differentoutputs, and may utilize a variety of available data in tracking theuser's eyes. As examples, eye tracking module 614 may utilize availabledata including eye tracking extrinsics and intrinsics, such as thegeometric arrangements of the eye-tracking camera 324 relative to thelight sources 326 and the head-mounted-unit 602; assumed eye dimensions704 such as a typical distance of approximately 4.7 mm between a user'scenter of cornea curvature and the average center of rotation of theuser's eye or typical distances between a user's center of rotation andcenter of perspective; and per-user calibration data 706 such as aparticular user's interpupillary distance. Additional examples ofextrinsics, intrinsics, and other information that may be employed bythe eye tracking module 614 are described in U.S. patent applicationSer. No. 15/497,726, filed Apr. 26, 2017, which is incorporated byreference herein in its entirety.

Image preprocessing module 710 may receive images from an eye camerasuch as eye camera 324 and may perform one or more preprocessing (i.e.,conditioning) operations on the received images. As examples, imagepreprocessing module 710 may apply a Gaussian blur to the images, maydown sample the images to a lower resolution, may applying an unsharpmask, may apply an edge sharpening algorithm, or may apply othersuitable filters that assist with the later detection, localization, andlabelling of glints, a pupil, or other features in the images from eyecamera 324. The image preprocessing module 710 may apply a low-passfilter or a morphological filter such as an open filter, which mayremove high-frequency noise such as from the pupillary boundary 516 a(see FIG. 5), thereby removing noise that may hinder pupil and glintdetermination. The image preprocessing module 710 may outputpreprocessed images to the pupil identification module 712 and to theglint detection and labeling module 714.

Pupil identification module 712 may receive preprocessed images from theimage preprocessing module 710 and may identify regions of those imagesthat include the user's pupil. The pupil identification module 712 may,in some embodiments, determine the coordinates of the position, orcoordinates, of the center, or centroid, of the user's pupil in the eyetracking images from camera 324. In at least some embodiments, pupilidentification module 712 may identify contours in eye tracking images(e.g., contours of pupil iris boundary), identify contour moments (i.e.,centers of mass), apply a starburst pupil detection and/or a canny edgedetection algorithm, reject outliers based on intensity values, identifysub-pixel boundary points, correct for eye-camera distortion (i.e.,distortion in images captured by eye camera 324), apply a random sampleconsensus (RANSAC) iterative algorithm to fit an ellipse to boundariesin the eye tracking images, apply a tracking filter to the images, andidentify sub-pixel image coordinates of the user's pupil centroid. Thepupil identification module 712 may output pupil identification data,which may indicate which regions of the preprocessing images module 712identified as showing the user's pupil, to glint detection and labelingmodule 714. The pupil identification module 712 may provide the 2Dcoordinates of the user's pupil (i.e., the 2D coordinates of thecentroid of the user's pupil) within each eye tracking image to glintdetection module 714. In at least some embodiments, pupil identificationmodule 712 may also provide pupil identification data of the same sortto coordinate system normalization module 718.

Pupil detection techniques, which may be utilized by pupilidentification module 712, are described in U.S. Patent Publication No.2017/0053165, published Feb. 23, 2017 and in U.S. Patent Publication No.2017/0053166, published Feb. 23, 2017, each of which is incorporated byreference herein in its entirety.

Glint detection and labeling module 714 may receive preprocessed imagesfrom module 710 and pupil identification data from module 712. Glintdetection module 714 may use this data to detect and/or identify glints(i.e., reflections off of the user's eye of the light from light sources326) within regions of the preprocessed images that show the user'spupil. As an example, the glint detection module 714 may search forbright regions within the eye tracking image, sometimes referred toherein as “blobs” or local intensity maxima, that are in the vicinity ofthe user's pupil. In at least some embodiments, the glint detectionmodule 714 may rescale (e.g., enlarge) the pupil ellipse to encompassadditional glints. The glint detection module 714 may filter glints bysize and/or by intensity. The glint detection module 714 may alsodetermine the 2D positions of each of the glints within the eye trackingimage. In at least some examples, the glint detection module 714 maydetermine the 2D positions of the glints relative to the user's pupil,which may also be referred to as the pupil-glint vectors. Glintdetection and labeling module 714 may label the glints and output thepreprocessing images with labeled glints to the 3D cornea centerestimation module 716. Glint detection and labeling module 714 may alsopass along data such as preprocessed images from module 710 and pupilidentification data from module 712.

Pupil and glint detection, as performed by modules such as modules 712and 714, may use any suitable techniques. As examples, edge detectionmay be applied to the eye image to identify glints and pupils. Edgedetection may be applied by various edge detectors, edge detectionalgorithms, or filters. For example, a Canny Edge detector may beapplied to the image to detect edges such as in lines of the image.Edges may include points located along a line that correspond to thelocal maximum derivative. For example, the pupillary boundary 516 a (seeFIG. 5) may be located using a Canny edge detector. With the location ofthe pupil determined, various image processing techniques may be used todetect the “pose” of the pupil 116. Determining an eye pose of an eyeimage may also be referred to as detecting an eye pose of the eye image.The pose may also be referred to as the gaze, pointing direction, or theorientation of the eye. For example, the pupil may be looking leftwardstowards an object, and the pose of the pupil could be classified as aleftwards pose. Other methods may be used to detect the location of thepupil or glints. For example, a concentric ring may be located in an eyeimage using a Canny Edge detector. As another example, anintegro-differential operator may be used to find the pupillary orlimbus boundaries of the iris. For example, the Daugmanintegro-differential operator, the Hough transform, or other irissegmentation techniques may be used to return a curve that estimates theboundary of the pupil or the iris.

3D cornea center estimation module 716 may receive preprocessed imagesincluding detected glint data and pupil identification data from modules710, 712, 714. 3D cornea center estimation module 716 may use these datato estimate the 3D position of the user's cornea. In some embodiments,the 3D cornea center estimation module 716 may estimate the 3D positionof an eye's center of cornea curvature or a user's corneal sphere, i.e.,the center of an imaginary sphere having a surface portion generallycoextensive with the user's cornea. The 3D cornea center estimationmodule 716 may provide data indicating the estimated 3D coordinates ofthe corneal sphere and/or user's cornea to the coordinate systemnormalization module 718, the optical axis determination module 722,and/or the light-field render controller 618. Further details of theoperation of the 3D cornea center estimation module 716 are providedherein in connection with FIGS. 8A-8E. Techniques for estimating thepositions of eye features such as a cornea or corneal sphere, which maybe utilized by 3D cornea center estimation module 716 and other modulesin the wearable systems of the present disclosure are discussed in U.S.patent application Ser. No. 15/497,726, filed Apr. 26, 2017, which isincorporated by reference herein in its entirety.

Coordinate system normalization module 718 may optionally (as indicatedby its dashed outline) be included in eye tracking module 614.Coordinate system normalization module 718 may receive data indicatingthe estimated 3D coordinates of the center of the user's cornea (and/orthe center of the user's corneal sphere) from the 3D cornea centerestimation module 716 and may also receive data from other modules.Coordinate system normalization module 718 may normalize the eye cameracoordinate system, which may help to compensate for slippages of thewearable device (e.g., slippages of the head-mounted component from itsnormal resting position on the user's head, which may be identified byregistration observer 620). Coordinate system normalization module 718may rotate the coordinate system to align the z-axis (i.e., the vergencedepth axis) of the coordinate system with the cornea center (e.g., asindicated by the 3D cornea center estimation module 716) and maytranslate the camera center (i.e., the origin of the coordinate system)to a predetermined distance away from the cornea center such as 30 mm(i.e., module 718 may enlarge or shrink the eye tracking image dependingon whether the eye camera 324 was determined to be nearer or furtherthan the predetermined distance). With this normalization process, theeye tracking module 614 may be able to establish a consistentorientation and distance in the eye tracking data, relativelyindependent of variations of headset positioning on the user's head.Coordinate system normalization module 718 may provide 3D coordinates ofthe center of the cornea (and/or corneal sphere), pupil identificationdata, and preprocessed eye tracking images to the 3D pupil centerlocator module 720. Further details of the operation of the coordinatesystem normalization module 718 are provided herein in connection withFIGS. 9A-9C.

3D pupil center locator module 720 may receive data, in the normalizedor the unnormalized coordinate system, including the 3D coordinates ofthe center of the user's cornea (and/or corneal sphere), pupil locationdata, and preprocessed eye tracking images. 3D pupil center locatormodule 720 may analyze such data to determine the 3D coordinates of thecenter of the user's pupil in the normalized or unnormalized eye cameracoordinate system. The 3D pupil center locator module 720 may determinethe location of the user's pupil in three-dimensions based on the 2Dposition of the pupil centroid (as determined by module 712), the 3Dposition of the cornea center (as determined by module 716), assumed eyedimensions 704 such as the size of the a typical user's corneal sphereand the typical distance from the cornea center to the pupil center, andoptical properties of eyes such as the index of refraction of the cornea(relative to the index of refraction of air) or any combination ofthese. Further details of the operation of the 3D pupil center locatormodule 720 are provided herein in connection with FIGS. 9D-9G.Techniques for estimating the positions of eye features such as a pupil,which may be utilized by 3D pupil center locator module 720 and othermodules in the wearable systems of the present disclosure are discussedin U.S. patent application Ser. No. 15/497,726, filed Apr. 26, 2017,which is incorporated by reference herein in its entirety.

Optical axis determination module 722 may receive data from modules 716and 720 indicating the 3D coordinates of the center of the user's corneaand the user's pupil. Based on such data, the optical axis determinationmodule 722 may identify a vector from the position of the cornea center(i.e., from the center of the corneal sphere) to the center of theuser's pupil, which may define the optical axis of the user's eye.Optical axis determination module 722 may provide outputs specifying theuser's optical axis to modules 724, 728, 730, and 732, as examples.

Center of rotation (CoR) estimation module 724 may receive data frommodule 722 including parameters of the optical axis of the user's eye(i.e., data indicating the direction of the optical axis in a coordinatesystem with a known relation to the head-mounted unit 602). CoRestimation module 724 may estimate the center of rotation of a user'seye (i.e., the point around which the user's eye rotates when the usereye rotates left, right, up, and/or down). While eyes may not rotateperfectly around a singular point, assuming a singular point may besufficient. In at least some embodiments, CoR estimation module 724 mayestimate an eye's center of rotation by moving from the center of thepupil (identified by module 720) or the center of curvature of thecornea (as identified by module 716) toward the retina along the opticalaxis (identified by module 722) a particular distance. This particulardistance may be an assumed eye dimension 704. As one example, theparticular distance between the center of curvature of the cornea andthe CoR may be approximately 4.7 mm. This distance may be varied for aparticular user based on any relevant data including the user's age,sex, vision prescription, other relevant characteristics, etc.

In at least some embodiments, the CoR estimation module 724 may refineits estimate of the center of rotation of each of the user's eyes overtime. As an example, as time passes, the user will eventually rotatetheir eyes (to look somewhere else, at something closer, further, orsometime left, right, up, or down) causing a shift in the optical axisof each of their eyes. CoR estimation module 724 may then analyze two(or more) optical axes identified by module 722 and locate the 3D pointof intersection of those optical axes. The CoR estimation module 724 maythen determine the center of rotation lies at that 3D point ofintersection. Such a technique may provide for an estimate of the centerof rotation, with an accuracy that improves over time. Varioustechniques may be employed to increase the accuracy of the CoRestimation module 724 and the determined CoR positions of the left andright eyes. As an example, the CoR estimation module 724 may estimatethe CoR by finding the average point of intersection of optical axesdetermined for various different eye poses over time. As additionalexamples, module 724 may filter or average estimated CoR positions overtime, may calculate a moving average of estimated CoR positions overtime, and/or may apply a Kalman filter and known dynamics of the eyesand eye tracking system to estimate the CoR positions over time. As aspecific example, module 724 may calculate a weighted average ofdetermined points of optical axes intersection and assumed CoR positions(such as 4.7 mm from an eye's center of cornea curvature), such that thedetermined CoR may slowly drift from an assumed CoR position (i.e., 4.7mm behind an eye's center of cornea curvature) to a slightly differentlocation within the user's eye over time as eye tracking data for theuser is obtain and thereby enables per-user refinement of the CoRposition.

Interpupillary distance (IPD) estimation module 726 may receive datafrom CoR estimation module 724 indicating the estimated 3D positions ofthe centers of rotation of the user's left and right eyes. IPDestimation module 726 may then estimate a user's IPD by measuring the 3Ddistance between the centers of rotation of the user's left and righteyes. In general, the distance between the estimated CoR of the user'sleft eye and the estimated CoR of the user's right eye may be roughlyequal to the distance between the centers of a user's pupils, when theuser is looking at optical infinity (i.e., the optical axes of theuser's eyes are substantially parallel to one another), which is thetypical definition of interpupillary distance (IPD). A user's IPD may beused by various components and modules in the wearable system. Asexample, a user's IPD may be provided to registration observer 620 andused in assessing how well the wearable device is aligned with theuser's eyes (e.g., whether the left and right display lenses areproperly spaced in accordance with the user's IPD). As another example,a user's IPD may be provided to vergence depth estimation module 728 andbe used in determining a user's vergence depth. Module 726 may employvarious techniques, such as those discussed in connection with CoRestimation module 724, to increase the accuracy of the estimated IPD. Asexamples, IPD estimation module 724 may apply filtering, averaging overtime, weighted averaging including assumed IPD distances, Kalmanfilters, etc. as part of estimating a user's IPD in an accurate manner.

Vergence depth estimation module 728 may receive data from variousmodules and submodules in the eye tracking module 614 (as shown inconnection with FIG. 7A). In particular, vergence depth estimationmodule 728 may employ data indicating estimated 3D positions of pupilcenters (e.g., as provided by module 720 described above), one or moredetermined parameters of optical axes (e.g., as provided by module 722described above), estimated 3D positions of centers of rotation (e.g.,as provided by module 724 described above), estimated IPD (e.g.,Euclidean distance(s) between estimated 3D positions of centers ofrotations) (e.g., as provided by module 726 described above), and/or oneor more determined parameters of optical and/or visual axes (e.g., asprovided by module 722 and/or module 730 described below). Vergencedepth estimation module 728 may detect or otherwise obtain a measure ofa user's vergence depth, which may be the distance from the user atwhich the user's eyes are focused. As examples, when the user is lookingat an object three feet in front of them, the user's left and right eyeshave a vergence depth of three feet; and, while when the user is lookingat a distant landscape (i.e., the optical axes of the user's eyes aresubstantially parallel to one another such that the distance between thecenters of the user's pupils may be roughly equal to the distancebetween the centers of rotation of the user's left and right eyes), theuser's left and right eyes have a vergence depth of infinity. In someimplementations, the vergence depth estimation module 728 may utilizedata indicating the estimated centers of the user's pupils (e.g., asprovided by module 720) to determine the 3D distance between theestimated centers of the user's pupils. The vergence depth estimationmodule 728 may obtain a measure of vergence depth by comparing such adetermined 3D distance between pupil centers to estimated IPD (e.g.,Euclidean distance(s) between estimated 3D positions of centers ofrotations) (e.g., as indicated by module 726 described above). Inaddition to the 3D distance between pupil centers and estimated IPD, thevergence depth estimation module 728 may utilize known, assumed,estimated, and/or determined geometries to calculate vergence depth. Asan example, module 728 may combine 3D distance between pupil centers,estimated IPD, and 3D CoR positions in a trigonometric calculation toestimate (i.e., determine) a user's vergence depth. Indeed, anevaluation of such a determined 3D distance between pupil centersagainst estimated IPD may serve to indicate a measure of the user'scurrent vergence depth relative to optical infinity. In some examples,the vergence depth estimation module 728 may simply receive or accessdata indicating an estimated 3D distance between the estimated centersof the user's pupils for purposes of obtaining such a measure ofvergence depth. In some embodiments, the vergence depth estimationmodule 728 may estimate vergence depth by comparing a user's left andright optical axis. In particular, vergence depth estimation module 728may estimate vergence depth by locating the distance from a user atwhich the user's left and right optical axes intersect (or whereprojections of the user's left and right optical axes on a plane such asa horizontal plane intersect). Module 728 may utilize a user's IPD inthis calculation, by setting the zero depth to be the depth at which theuser's left and right optical axes are separated by the user's IPD. Inat least some embodiments, vergence depth estimation module 728 maydetermine vergence depth by triangulating eye tracking data togetherwith known or derived spatial relationships.

In some embodiments, vergence depth estimation module 728 may estimate auser's vergence depth based on the intersection of the user's visualaxes (instead of their optical axes), which may provide a more accurateindication of the distance at which the user is focused on. In at leastsome embodiments, eye tracking module 614 may include optical to visualaxis mapping module 730. As discussed in further detail in connectionwith FIG. 10, a user's optical and visual axis are generally notaligned. A visual axis is the axis along which a person is looking,while an optical axis is defined by the center of that person's lens andpupil, and may go through the center of the person's retina. Inparticular, a user's visual axis is generally defined by the location ofthe user's fovea, which may be offset from the center of a user'sretina, thereby resulting in different optical and visual axis. In atleast some of these embodiments, eye tracking module 614 may includeoptical to visual axis mapping module 730. Optical to visual axismapping module 730 may correct for the differences between a user'soptical and visual axis and provide information on the user's visualaxis to other components in the wearable system, such as vergence depthestimation module 728 and light-field render controller 618. In someexamples, module 730 may use assumed eye dimensions 704 including atypical offset of approximately 5.2° inwards (nasally, towards a user'snose) between an optical axis and a visual axis. In other words, module730 may shift a user's left optical axis (nasally) rightwards by 5.2°towards the nose and a user's right optical axis (nasally) leftwards by5.2° towards the nose in order to estimate the directions of the user'sleft and right optical axes. In other examples, module 730 may utilizeper-user calibration data 706 in mapping optical axes (e.g., asindicated by module 722 described above) to visual axes. As additionalexamples, module 730 may shift a user's optical axes nasally by between4.0° and 6.5°, by between 4.5° and 6.0°, by between 5.0° and 5.4°, etc.,or any ranges formed by any of these values. In some arrangements, themodule 730 may apply a shift based at least in part upon characteristicsof a particular user such as their age, sex, vision prescription, orother relevant characteristics and/or may apply a shift based at leastin part upon a calibration process for a particular user (i.e., todetermine a particular user's optical-visual axis offset). In at leastsome embodiments, module 730 may also shift the origins of the left andright optical axes to correspond with the user's CoP (as determined bymodule 732) instead of the user's CoR.

Optional center of perspective (CoP) estimation module 732, whenprovided, may estimate the location of the user's left and right centersof perspective (CoP). A CoP may be a useful location for the wearablesystem and, in at least some embodiments, is a position just in front ofa pupil. In at least some embodiments, CoP estimation module 732 mayestimate the locations of a user's left and right centers of perspectivebased on the 3D location of a user's pupil center, the 3D location of auser's center of cornea curvature, or such suitable data or anycombination thereof. As an example, a user's CoP may be approximately5.01 mm in front of the center of cornea curvature (i.e., 5.01 mm fromthe corneal sphere center in a direction that is towards the eye'scornea and that is along the optical axis) and may be approximately 2.97mm behind the outer surface of a user's cornea, along the optical orvisual axis. A user's center of perspective may be just in front of thecenter of their pupil. As examples, a user's CoP may be less thanapproximately 2.0 mm from the user's pupil, less than approximately 1.0mm from the user's pupil, or less than approximately 0.5 mm from theuser's pupil or any ranges between any of these values. As anotherexample, the center of perspective may correspond to a location withinthe anterior chamber of the eye. As other examples, the CoP may bebetween 1.0 mm and 2.0 mm, about 1.0 mm, between 0.25 mm and 1.0 mm,between 0.5 mm and 1.0 mm, or between 0.25 mm and 0.5 mm.

The center of perspective described herein (as a potentially desirableposition for a pinhole of a render camera and an anatomical position ina user's eye) may be a position that serves to reduce and/or eliminateundesired parallax shifts. In particular, the optical system of a user'seye is very roughly equivalent to theoretical system formed by a pinholein front of a lens, projecting onto a screen, with the pinhole, lens,and screen roughly corresponding to a user's pupil/iris, lens, andretina, respectively. Moreover, it may be desirable for there to belittle or no parallax shift when two point light sources (or objects) atdifferent distances from the user's eye are rigidly rotated about theopening of the pinhole (e.g., rotated along radii of curvature equal totheir respective distance from the opening of the pinhole). Thus, itwould seem that the CoP should be located at the center of the pupil ofan eye (and such a CoP may be used in some embodiments). However, thehuman eye includes, in addition to the lens and pinhole of the pupil, acornea that imparts additional optical power to light propagating towardthe retina). Thus, the anatomical equivalent of the pinhole in thetheoretical system described in this paragraph may be a region of theuser's eye positioned between the outer surface of the cornea of theuser's eye and the center of the pupil or iris of the user's eye. Forinstance, the anatomical equivalent of the pinhole may correspond to aregion within the anterior chamber of a user's eye. For various reasonsdiscussed herein, it may be desired to set the CoP to such a positionwithin the anterior chamber of the user's eye.

As discussed above, eye tracking module 614 may provide data, such asestimated 3D positions of left and right eye centers of rotation (CoR),vergence depth, left and right eye optical axis, 3D positions of auser's eye, 3D positions of a user's left and right centers of corneacurvature, 3D positions of a user's left and right pupil centers, 3Dpositions of a user's left and right center of perspective, a user'sIPD, etc., to other components, such as light-field render controller618 and registration observer 620, in the wearable system. Eye trackingmodule 614 may also include other submodules that detect and generatedata associated with other aspects of a user's eye. As examples, eyetracking module 614 may include a blink detection module that provides aflag or other alert whenever a user blinks and a saccade detectionmodule that provides a flag or other alert whenever a user's eyesaccades (i.e., quickly shifts focus to another point).

Example of a Render Controller

A detailed block diagram of an example light-field render controller 618is shown in FIG. 7B. As shown in FIGS. 6 and 7B, render controller 618may receive eye tracking information from eye tracking module 614 andmay provide outputs to render engine 622, which may generate images tobe displayed for viewing by a user of the wearable system. As examples,render controller 618 may receive information regarding a vergencedepth, left and right eye centers of rotation (and/or centers ofperspective), and other eye data such as blink data, saccade data, etc.

Depth plane selection module 750 may receive vergence depth informationand, based on such data, may cause render engine 622 to provide contentto a user, with the content appearing to be located on a particulardepth plane (i.e., at a particular accommodation or focal distance). Asdiscussed in connection with FIG. 4, a wearable system may include aplurality of discrete depth planes formed by a plurality of waveguides,each conveying image information with a varying level of wavefrontcurvature. In some embodiments, a wearable system may include one ormore variable depth planes, such as an optical element that conveysimage information with a level of wavefront curvature that varies overtime. In these and other embodiments, depth plane selection module 750may cause render engine 622 to convey content to a user at a selecteddepth (i.e., cause render engine 622 to direct display 220 to switchdepth planes), based in part of the user's vergence depth. In at leastsome embodiments, depth plane selection module 750 and render engine 622may render content at different depths and also generate and/or providedepth plane selection data to display hardware such as display 220.Display hardware such as display 220 may perform an electrical depthplane switching in response to depth plane selection data (which may becontrol signals) generated by and/or provided by modules such as depthplane selection module 750 and render engine 622.

In general, it may be desirable for depth plane selection module 750 toselect a depth plane matching the user's current vergence depth, suchthat the user is provided with accurate accommodation cues. However, itmay also be desirable to switch depth planes in a discreet andunobtrusive manner. As examples, it may be desirable to avoid excessiveswitching between depth planes and/or it may be desire to switch depthplanes at a time when the user is less likely to notice the switch, suchas during a blink or eye saccade.

Hysteresis band crossing detection module 752 may help to avoidexcessive switching between depth planes, particularly when a user'svergence depth fluctuates at the midpoint or transition point betweentwo depth planes. In particular, module 752 may cause depth planeselection module 750 to exhibit hysteresis in its selection of depthplanes. As an example, modules 752 may cause depth plane selectionmodule 750 to switch from a first farther depth plane to a second closerdepth plane only after a user's vergence depth passes a first threshold.Similarly, module 752 may cause depth plane selection module 750 (whichmay in turn direct displays such as display 220) to switch to the firstfarther depth plane only after the user's vergence depth passes a secondthreshold that is farther from the user than the first threshold. In theoverlapping region between the first and second thresholds, module 750may cause depth plane selection module 750 to maintain whichever depthplane is currently select as the selected depth plane, thus avoidingexcessive switching between depth planes.

Ocular event detection module 750 may receive other eye data from theeye tracking module 614 of FIG. 7A and may cause depth plane selectionmodule 750 to delay some depth plane switches until an ocular eventoccurs. As an example, ocular event detection module 750 may cause depthplane selection module 750 to delay a planned depth plane switch until auser blink is detected; may receive data from a blink detectioncomponent in eye tracking module 614 that indicates when the user iscurrently blinking; and, in response, may cause depth plane selectionmodule 750 to execute the planned depth plane switch during the blinkevent (such by causing module 750 to direct display 220 to execute thedepth plane switch during the blink event). In at least someembodiments, the wearable system may be able to shift content onto a newdepth plane during a blink event such that the user is unlikely toperceive the shift. As another example, ocular event detection module750 may delay planned depth plane switches until an eye saccade isdetected. As discussed in connection with eye blinks, such as anarrangement may facilitate the discrete shifting of depth planes.

If desired, depth plane selection module 750 may delay planned depthplane switches only for a limited period of time before executing thedepth plane switch, even in the absence of an ocular event. Similarly,depth plane selection module 750 may execute a depth plane switch whenthe user's vergence depth is substantially outside of acurrently-selected depth plane (i.e., when the user's vergence depth hasexceeded a predetermined threshold beyond the regular threshold for adepth plane switch), even in the absence of an ocular event. Thesearrangements may help ensure that ocular event detection module 754 doesnot indefinitely delay depth plane switches and does not delay depthplane switches when a large accommodation error is present.

Render camera controller 758 may provide information to render engine622 indicating where the user's left and right eyes are. Render engine622 may then generate content by simulating cameras at the positions ofthe user's left and right eyes and generating content based on theperspectives of the simulated cameras. As discussed above, the rendercamera is a simulated camera for use in rendering virtual image contentpossibly from a database of objects in a virtual world. The objects mayhave locations and orientations relative to the user or wearer andpossibly relative to real objects in the environment surrounding theuser or wearer. The render camera may be included in a render engine torender virtual images based on the database of virtual objects to bepresented to the eye. The virtual images may be rendered as if takenfrom the perspective the user or wearer. For example, the virtual imagesmay be rendered as if captured by a camera (corresponding to the “rendercamera”) having an aperture, lens, and detector viewing the objects inthe virtual world. The virtual images are taken from the perspective ofsuch a camera having a position of the “render camera.” For example, thevirtual images may be rendered as if captured from the perspective of acamera having a specific location with respect to the user's or wearer'seye so as to provide images that appear to be from the perspective ofthe user or wearer. In some implementations, the images are rendered asif captured from the perspective of a camera having an aperture at aspecific location with respect to the user's or wearer's eye (such asthe center of perspective or center of rotation as discussed herein, orelsewhere).

Render camera controller 758 may determine the positions of the left andright cameras based on the left and right eye centers of rotation (CoR),determined by CoR estimation module 724, and/or based on the left andright eye centers of perspective (CoP), determined by CoP estimationmodule 732. In some embodiments, render camera controller 758 may switchbetween the CoR and CoP locations based on various factors. As examples,the render camera controller 758 may, in various modes, register therender camera to the CoR locations at all times, register the rendercamera to the CoP locations at all times, toggle or discretely switchbetween registering the render camera to the CoR locations andregistering the render camera to the CoP locations over time based onvarious factors, or dynamically register the render camera to any of arange of different positions along the optical (or visual) axis betweenthe CoR and CoP locations over time based on various factors. The CoRand CoP positions may optionally pass through smoothing filter 756 (inany of the aforementioned modes for render camera positioning) which mayaverage the CoR and CoP locations over time to reduce noise in thesepositions and prevent jitter in the render simulated render cameras.

In at least some embodiments, the render camera may be simulated as apinhole camera with the pinhole disposed at the position of theestimated CoR or CoP identified by eye tracking module 614. As the CoPis offset from the CoR, the location of the render camera and itspinhole both shift as the user's eye rotates, whenever the rendercamera's position is based on a user's CoP. In contrast, whenever therender camera's position is based on a user's CoR, the location of therender camera's pinhole does not move with eye rotations, although therender camera (which is behind the pinhole) may, in some embodiments,move with eye rotation. In other embodiments where the render camera'sposition is based on a user's CoR, the render camera may not move (i.e.,rotate) with a user's eye.

Example of a Registration Observer

A block diagram of an example registration observer 620 is shown in FIG.7C. As shown in FIGS. 6, 7A, and 7C, registration observer 620 mayreceive eye tracking information from eye tracking module 614 (FIGS. 6and 7A). As examples, registration observer 620 may receive informationon a user's left and right eye centers of rotation (e.g., thethree-dimensional positions of the user's left and right eye centers ofrotations, which may be on a common coordinate system or have a commonframe of reference with the head-mounted display system 600). As otherexamples, registration observer 620 may receive display extrinsics, fittolerances, and an eye-tracking valid indicator. The display extrinsicsmay include information on the display (e.g., display 200 of FIG. 2)such as the field of view of the display, the size of one or moredisplay surfaces, and the positions of the display surfaces relative tothe head-mounted display system 600. The fit tolerances may includeinformation on display registration volumes, which may indicate how farthe user's left and right eyes may move from nominal positions beforedisplay performance is impacted. In addition, the fit tolerances mayindicate the amount of display performance impact that is expected as afunction of the positions of the user's eyes.

As shown in FIG. 7C, registration observer 620 may include a 3Dpositional fit module 770. The positional fit module 770 may obtain andanalyze various pieces of data including, as examples, a left eye centerof rotation 3D position (e.g., CoR Left), a right eye center of rotation3D position (e.g., CoR Right), display extrinsics, and fit tolerances.The 3D positional fit module 770 may determine how far the user's leftand right eyes are from the respective left and right eye nominalpositions (e.g., may calculate 3D left error and 3D right error) and mayprovide the error distances (e.g., 3D left error and 3D right error) todevice 3D fit module 772.

3D positional fit module 770 may also compare the error distances to thedisplay extrinsics and the fit tolerances to determine if the users eyeare within a nominal volume, a partially-degraded volume (e.g., a volumein which the performance of display 220 is partially degraded), or in afully degraded or nearly fully degraded volume (e.g., a volume in whichdisplay 220 is substantially unable to provide content to the user'seyes). In at least some embodiments, 3D positional fit module 770 or 3Dfit module 772 may provide an output qualitatively describing the fit ofthe HMD on the user, such as the Quality of Fit output shown in FIG. 7C.As an example, module 770 may provide an output indicating whether thecurrent fit of the HMD on the user is good, marginal, or failed. A goodfit may correspond to a fit that enables the user to view at least acertain percentage of the image (such as 90%), a marginal fit may enablethe user to view at least a lower percentage of the image (such as 80%),while a failed fit may be a fit in which only an even lower percentageof the image is visible to the user.

As another example, the 3D positional fit module 770 and/or device 3Dfit module 772 may calculate a visible area metric, which may be apercentage of the overall area (or pixels) of images display by display220 that are visible to the user. Modules 770 and 772 may calculate thevisible area metric by evaluating the positions of the user's left andright eyes (e.g., which may be based on the centers of rotation of theuser's eyes) relative to display 220 and using one or more models (e.g.,a mathematical or geometric model), one or more look-up tables, or othertechniques or combinations of these and other techniques to determinewhat percentage of the images are visible to the user as a function ofthe positions of the user's eyes. Additionally, modules 770 and 772 maydetermine which regions or portions of the images display by display 220are expected to be visible to the user as a function of the positions ofthe user's eyes.

Registration observer 620 may also include a device 3D fit module 772.Module 772 may receive data from 3D positional fit module 770 and mayalso receive an eye tracking valid indicator, which may be provided byeye tracking module 614 and may indicate whether the eye tracking systemis currently tracking the positions of the user's eyes or if eyetracking data is unavailable or in an error condition (e.g., determinedto be no reliable). Device 3D fit module 772 may, if desired, modifyquality of fit data received from 3D positional fit module 770 dependingon the state of the eye tracking valid data. For example, if the datafrom the eye tracking system is indicated to not be available or to havean error, the device 3D fit module 772 may provide a notification thatthere is an error and/or not provide output to the user regarding fitquality or fit errors.

In at least some embodiments, registration observer 620 may providefeedback to users on the quality of fit as well as details of the natureand magnitude of the error. As examples, the head-mounted display systemmay provide feedback to the user during calibration or fitting processes(e.g., as part of a setup procedure) and may provide feedback duringoperation (e.g., if the fit degrades due to slippage, the registrationobserver 620 may prompt the user to readjust the head-mounted displaysystem). In some embodiments, the registration analysis may be performedautomatically (e.g., during use of the head-mounted display system) andthe feedback may be provided without user input. These are merelyillustrative examples.

Example of Locating a User's Cornea with an Eye Tracking System

FIG. 8A is a schematic diagram of an eye showing the eye's cornealsphere. As shown in FIG. 8A, a user's eye 810 may have a cornea 812, apupil 822, and a lens 820. The cornea 812 may have an approximatelyspherical shape, shown by corneal sphere 814. Corneal sphere 814 mayhave a center point 816, also referred to as a corneal center, and aradius 818. The semispherical cornea of a user's eye may curve aroundthe corneal center 816.

FIGS. 8B-8E illustrate an example of locating a user's corneal center816 using 3D cornea center estimation module 716 and eye tracking module614.

As shown in FIG. 8B, 3D cornea center estimation module 716 may receivean eye tracking image 852 that includes a corneal glint 854. The 3Dcornea center estimation module 716 may then simulate, in an eye cameracoordinate system 850, the known 3D positions of the eye camera 324 andlight source 326 (which may be based on data in eye tracking extrinsics& intrinsics database 702, assumed eye dimensions database 704, and/orper-user calibration data 706) in order to cast a ray 856 in the eyecamera coordinate system. In at least some embodiments, the eye cameracoordinate system 850 may have its origin at the 3D position of theeye-tracking camera 324.

In FIG. 8C, 3D cornea center estimation module 716 simulates a cornealsphere 814 a (which may be based on assumed eye dimensions from database704) and corneal curvature center 816 a at a first position. The 3Dcornea center estimation module 716 may then check to see whether thecorneal sphere 814 a would properly reflect light from the light source326 to the glint position 854. As shown in FIG. 8C, the first positionis not a match as the ray 860 a does not intersect light source 326.

Similarly in FIG. 8D, 3D cornea center estimation module 716 simulates acorneal sphere 814 b and corneal curvature center 816 b at a secondposition. The 3D cornea center estimation module 716 then checks to seewhether the corneal sphere 814 b properly reflects light from the lightsource 326 to the glint position 854. As shown in FIG. 8D, the secondposition is also not a match.

As shown in FIG. 8E, the 3D cornea center estimation module 716eventually is able to determine the correct position of the cornealsphere is corneal sphere 814 c and corneal curvature center 816 c. The3D cornea center estimation module 716 confirms the illustrated positionis correct by checking that light from source 326 will properly reflectoff of the corneal sphere and be imaged by camera 324 at the correctlocation of glint 854 on image 852. With this arrangement and with theknown 3D positions of the light source 326, the camera 324, and theoptical properties of the camera (focal length, etc.), the 3D corneacenter estimation module 716 may determine the 3D location of thecornea's center of curvature 816 (relative to the wearable system).

The processes described herein in connection with at least FIGS. 8C-8Emay effectively be an iterative, repetitious, or optimization process toidentify the 3D position of the user's cornea center. As such, any of aplurality of techniques (e.g., iterative, optimization techniques, etc.)may be used to efficiently and quickly prune or reduce the search spaceof possible positions. Moreover, in some embodiments, the system mayinclude two, three, four, or more light sources such as light source 326and some of all of these light sources may be disposed at differentpositions, resulting in multiple glints such as glint 854 located atdifferent positions on image 852 and multiple rays such as ray 856having different origins and directions. Such embodiments may enhancethe accuracy of the 3D cornea center estimation module 716, as themodule 716 may seek to identify a cornea position that results in someor all of the glints & rays being properly reflected between theirrespective light sources and their respective positions on image 852. Inother words and in these embodiments, the positions of some or all ofthe light sources may be relied upon in the 3D cornea positiondetermination (e.g., iterative, optimization techniques, etc.) processesof FIGS. 8B-8E.

Example of Normalizing the Coordinate System of Eye Tracking Images

FIGS. 9A-9C illustrate an example normalization of the coordinate systemof eye tracking images, by a component in the wearable system such ascoordinate system normalization module 718 of FIG. 7A. Normalizing thecoordinate system of eye tracking images relative to a user's pupillocation may compensate for slippage of the wearable system relative toa user's face (i.e., headset slippage) and such normalization mayestablish a consistent orientation and distance between eye trackingimages and a user's eyes.

As shown in FIG. 9A, coordinate system normalization module 718 mayreceive estimated 3D coordinates 900 of a user's center of cornealrotation and may receive un-normalized eye tracking images such as image852. Eye tracking image 852 and coordinates 900 may be in anun-normalized coordinate system 850 that is based on the location ofeye-tracking camera 324, as an example.

As a first normalization step, coordinate system normalization module718 may rotate coordinate system 850 into rotated coordinate system 902,such that the z-axis (i.e., the vergence depth axis) of the coordinatesystem may be aligned with a vector between the origin of the coordinatesystem and cornea center of curvature coordinates 900, as shown in FIG.9B. In particular, coordinate system normalization module 718 may rotateeye tracking image 850 into rotated eye tracking image 904, until thecoordinates 900 of the user's corneal center of curvature are normal tothe plane of the rotated image 904.

As a second normalization step, coordinate system normalization module718 may translate rotated coordinate system 902 into normalizedcoordinate system 910, such that cornea center of curvature coordinates900 are a standard, normalized distance 906 from the origin ofnormalized coordinate system 910, as shown in FIG. 9C. In particular,coordinate system normalization module 718 may translate rotated eyetracking image 904 into normalized eye tracking image 912. In at leastsome embodiments, the standard, normalized distance 906 may beapproximately 30 millimeters. If desired, the second normalization stepmay be performed prior to the first normalization step.

Example of Locating a User's Pupil Centroid with an Eye Tracking System

FIGS. 9D-9G illustrate an example of locating a user's pupil center(i.e., the center of a user's pupil 822 as shown in FIG. 8A) using 3Dpupil center locator module 720 and eye tracking module 614.

As shown in FIG. 9D, 3D pupil center locator module 720 may receive anormalized eye tracking image 912 that includes a pupil centroid 913(i.e., a center of a user's pupil as identified by pupil identificationmodule 712). The 3D pupil center locator module 720 may then simulatethe normalized 3D position 910 of eye camera 324 to cast a ray 914 inthe normalized coordinate system 910, through the pupil centroid 913.

In FIG. 9E, 3D pupil center locator module 720 may simulate a cornealsphere such as corneal sphere 901 having center of curvature 900 basedon data from 3D cornea center estimation module 716 (and as discussed inmore detail in connection with FIGS. 8B-8E). As an example, the cornealsphere 901 may be positioned in the normalized coordinate system 910based on the location of the center of curvature 816 c identified inconnection with FIG. 8E and based on the normalization processes ofFIGS. 9A-9C. Additionally, 3D pupil center locator module 720 mayidentify a first intersection 916 between ray 914 (i.e., a ray betweenthe origin of normalized coordinate system 910 and the normalizedlocation of a user's pupil) and the simulated cornea, as shown in FIG.9E.

As shown in FIG. 9F, 3D pupil center locator module 720 may determinepupil sphere 918 based on corneal sphere 901. Pupil sphere 918 may sharea common center of curvature with corneal sphere 901, but have a smallradius. 3D pupil center locator module 720 may determine a distancebetween cornea center 900 and pupil sphere 918 (i.e., a radius of pupilsphere 918) based on a distance between the corneal center and the pupilcenter. In some embodiments, the distance between a pupil center and acorneal center of curvature may be determined from assumed eyedimensions 704 of FIG. 7A, from eye tracking extrinsics and intrinsicsdatabase 702, and/or from per-user calibration data 706. In otherembodiments, the distance between a pupil center and a corneal center ofcurvature may be determined from per-user calibration data 706 of FIG.7A.

As shown in FIG. 9G, 3D pupil center locator module 720 may locate the3D coordinates of a user's pupil center based on variety of inputs. Asexamples, the 3D pupil center locator module 720 may utilize the 3Dcoordinates and radius of the pupil sphere 918, the 3D coordinates ofthe intersection 916 between a simulated cornea sphere 901 and a ray 914associated with a pupil centroid 913 in a normalized eye tracking image912, information on the index of refraction of a cornea, and otherrelevant information such as the index of refraction of air (which maybe stored in eye tracking extrinsics & intrinsics database 702) todetermine the 3D coordinates of the center of a user's pupil. Inparticular, the 3D pupil center locator module 720 may, in simulation,bend ray 916 into refracted ray 922 based on refraction differencebetween air (at a first index of refraction of approximately 1.00) andcorneal material (at a second index of refraction of approximately1.38). After taking into account refraction caused by the cornea, 3Dpupil center locator module 720 may determine the 3D coordinates of thefirst intersection 920 between refracted ray 922 and pupil sphere 918.3D pupil center locator module 720 may determine that a user's pupilcenter 920 is located at approximately the first intersection 920between refracted ray 922 and pupil sphere 918. With this arrangement,the 3D pupil center locator module 720 may determine the 3D location ofthe pupil center 920 (relative to the wearable system), in thenormalized coordinate system 910. If desired, the wearable system mayun-normalize the coordinates of the pupil center 920 into the originaleye camera coordinate system 850. The pupil center 920 may be usedtogether with the corneal curvature center 900 to determine, among otherthings, a user's optical axis using optical axis determination module722 and a user's vergence depth by vergence depth estimation module 728.

Example of Differences Between Optical and Visual Axes

As discussed in connection with optical to visual mapping module 730 ofFIG. 7A, a user's optical and visual axes are generally not aligned, duein part to a user's visual axis being defined by their fovea and thatfoveae are not generally in the center of a person's retina. Thus, whena person desires to concentrate on a particular object, the personaligns their visual axis with that object to ensure that light from theobject falls on their fovea while their optical axis (defined by thecenter of their pupil and center of curvature of their cornea) isactually slightly offset from that object. FIG. 10 is an example of aneye 1000 illustrating the eye's optical axis 1002, the eye's visual axis1004, and the offset between these axes. Additionally, FIG. 10illustrates the eye's pupil center 1006, the eye's center of corneacurvature 1008, and the eye's average center of rotation (CoR) 1010. Inat least some populations, the eye's center of cornea curvature 1008 maylie approximately 4.7 mm in front, as indicated by dimension 1012, ofthe eye's average center of rotation (CoR) 1010. Additionally, the eye'scenter of perspective 1014 may lie approximately 5.01 mm in front of theeye's center of cornea curvature 1008, about 2.97 mm behind the outersurface 1016 of the user's cornea, and/or just in front of the user'spupil center 1006 (e.g., corresponding to a location within the anteriorchamber of eye 1000). As additional examples, dimension 1012 may between3.0 mm and 7.0 mm, between 4.0 and 6.0 mm, between 4.5 and 5.0 mm, orbetween 4.6 and 4.8 mm or any ranges between any values and any valuesin any of these ranges. The eye's center of perspective (CoP) 1014 maybe a useful location for the wearable system as, in at least someembodiments, registering a render camera at the CoP may help to reduceor eliminate parallax artifacts.

FIG. 10 also illustrates such a within a human eye 1000 with which thepinhole of a render camera may be aligned. As shown in FIG. 10, thepinhole of a render camera may be registered with a location 1014 alongthe optical axis 1002 or visual axis 1004 of the human eye 1000 closerto the outer surface of the cornea than both (a) the center of the pupilor iris 1006 and (b) the center of cornea curvature 1008 of the humaneye 1000. For example, as shown in FIG. 10, the pinhole of a rendercamera may be registered with a location 1014 along the optical axis1002 of the human eye 1000 that is about 2.97 millimeters rearward fromthe outer surface of the cornea 1016 and about 5.01 millimeters forwardfrom the center of cornea curvature 1008. The location 1014 of thepinhole of the render camera and/or the anatomical region of the humaneye 1000 to which the location 1014 corresponds may be seen asrepresenting the center of perspective of the human eye 1000. Theoptical axis 1002 of the human eye 1000 as shown in FIG. 10 representsthe most direct line through the center of cornea curvature 1008 and thecenter of the pupil or iris 1006. The visual axis 1004 of the human eye1000 differs from the optical axis 1002, as it represents a lineextending from the fovea of the human eye 1000 to the center of thepupil or iris 1006.

Example Processes of Rendering Content and Checking Registration Basedon Eye Tracking

FIG. 11 is a process flow diagram of an example method 1100 for usingeye tracking in rendering content and providing feedback on registrationin a wearable device. The method 1100 may be performed by the wearablesystem described herein. Embodiments of the method 1100 may be used bythe wearable system to render content and provide feedback onregistration (i.e., fit of the wearable device to the user) based ondata from an eye tracking system.

At block 1110, the wearable system may capture images of a user's eye oreyes. The wearable system may capture eye images using one or more eyecameras 324, as shown at least in the example of FIG. 3. If desired, thewearable system may also include one or more light sources 326configured to shine IR light on a user's eyes and produce correspondingglints in the eye images captured by eye cameras 324. As discussedherein, the glints may be used by an eye tracking module 614 to derivevarious pieces of information about a user's eye including where the eyeis looking.

At block 1120, the wearable system may detect glints and pupils in theeye images captured in block 1110. As an example, block 1120 may includeprocessing the eye images by glint detection & labeling module 714 toidentify the two-dimensional positions of glints in the eye images andprocessing the eye images by pupil identification module 712 to identifythe two-dimensional positions of pupils in the eye images.

At block 1130, the wearable system may estimate the three-dimensionalpositions of a user's left and right corneas relative to the wearablesystem. As an example, the wearable system may estimate the positions ofthe center of curvature of a user's left and right corneas as well asthe distances between those centers of curvature and the user's left andright corneas. Block 1130 may involve 3D cornea center estimation module716 identifying the position of the centers of curvature as describedherein at least in connection with FIGS. 7A and 8A-8E.

At block 1140, the wearable system may estimate the three-dimensionalpositions of a user's left and right pupil centers relative to thewearable system. As an example, the wearable system and 3D pupil centerlocator module 720 in particular, may estimate the positions of theuser's left and right pupil centers as described at least in connectionwith FIGS. 7A and 9D-9G, as part of block 1140.

At block 1150, the wearable system may estimate the three-dimensionalpositions of a user's left and right centers or rotation (CoR) relativeto the wearable system. As an example, the wearable system and CoRestimation module 724 in particular, may estimate the positions of theCoR for the user's left and right eyes as described at least inconnection with FIGS. 7A and 10. As a particular example, the wearablesystem may find the CoR of an eye by walking back along the optical axisfrom the center of curvature of a cornea towards the retina.

At block 1160, the wearable system may estimate a user's IPD, vergencedepth, center of perspective (CoP), optical axis, visual axis, and otherdesired attributes from eye tracking data. As examples, IPD estimationmodule 726 may estimate a user's IPD by comparing the 3D positions ofthe left and right CoRs, vergence depth estimation module 728 mayestimate a user's depth by finding an intersection (or nearintersection) of the left and right optical axes or an intersection ofthe left and right visual axes, optical axis determination module 722may identify the left and right optical axes over time, optical tovisual axis mapping module 730 may identify the left and right visualaxes over time, and the CoP estimation module 732 may identify the leftand right centers of perspective, as part of block 1160.

At block 1170, the wearable system may render content and may,optionally, provide feedback on registration (i.e., fit of the wearablesystem to the user's head) based in part on the eye tracking dataidentified in blocks 1120-1160. As an example, the wearable system mayidentify a suitable location for a render camera and then generatecontent for a user based on the render camera's location, as discussedin connection with light-field render controller 618, FIG. 7B, andrender engine 622. As another example, the wearable system may determineif it is properly fitted to the user, or has slipped from its properlocation relative to the user, and may provide optional feedback to theuser indicating whether the fit of the device needs adjustment, asdiscussed in connection with registration observer 620 and as discussedin connection with block 1608 of FIG. 16. In some embodiments, thewearable system may adjust rendered content based on improper or lessthan ideal registration in an attempt to reduce, minimize or compensatefor the effects of improper or mis-registration, as discussed inconnection with block 1610 of FIG. 16.

Overview of Device Registration

In order for the wearable system 200 described herein to output imagesof high perceived image quality, the display 220 of the wearable system200 (FIG. 2) is preferably properly fitted to a user (e.g., positionedand oriented with respect to the user's head such that the inputs andoutputs of system 200 interface appropriately with correspondingportions of the user's head and such that the device is stable andcomfortable to wear and use). As an example, for display 220 to providevisual content to a user's eyes, the display 220 is preferably situatedin front of the user's eyes and, depending on the relevant properties ofthe display 220, the user's eyes are preferably situated in a particularvolume (see, e.g., the further discussion associated with FIGS. 13A and13B). As additional examples, the speaker 240 is preferably situatednear, on, or in the user's ears to provide high-quality audio content tothe user, audio sensor (e.g., a microphone) 232 is preferably situatedin a particular area to receive sound from the user, and inward-facingimaging system 462 (which may include one or more cameras 324 and one ormore infrared light sources 326) is preferably properly situated in aposition and orientation to obtain clear, unobstructed images of auser's eyes (which may be part of an eye tracking system). These aremerely examples of various reasons why wearable system 200 arepreferably properly fitted to users.

In order to ensure the wearable system 200 is properly registered to auser, the wearable system 200 may include a registration observer suchas registration observer 620 of FIG. 6. In some embodiments, theproperly registered wearable system 200 includes a display that ispositioned so that one or more eyes of the user are able to receivesufficient image light to see substantially the entirety of the field ofview provided by the display 220 of the wearable display system 200. Forexample, a properly registered display may allow an image to be seenacross about 80% or more, about 85% or more, about 90% or more, or about95% or more of the field of view of the display with a brightnessuniformity of 80% or more, about 85% or more, about 90% or more, orabout 95% or more. It will be appreciated that the brightness uniformitymay be equal to 100% times the minimum luminance divided by the maximumluminance across the entirety of the field of view of the display(100%×L_(min)/L_(max)), when the display is displaying the same contentthroughout the field of view.

The registration observer 620 may determine how the wearable system 200is fitted on the user (e.g., if the display 220 of the wearable system200 is positioned on the user properly) using various sensors. As anexample, the registration observer 620 may use an inward-facing imagingsystem 462, which may include an eye tracking system, to determine howrelevant parts of the wearable system 200 are spatially oriented withrespect to the user and, in particular, the user's eyes, ears, mouth, orother parts that interface with the wearable system 200.

The registration observer 620 may assist with a calibration process,such an initial or subsequent configuration or setup of the wearablesystem 200 for a particular user. As an example, registration observer620 may provide feedback to a user during configuration or setup of thewearable system 200 for that particular user. Additionally oralternatively, the registration observer 620 may continuously, orintermittently, monitor registration of the wearable system 200 on auser to check for continued proper registration during use and mayprovide user feedback on the fly. Registration observer 620 may provideuser feedback, either as part of a configuration process or as part ofregistration monitoring during use, that indicates when the wearablesystem 200 is properly registered and when the wearable system 200 isnot properly registered. The registration observer 620 may also provideparticular recommendations for how the user may correct anymisregistration and achieve proper registration. As examples, theregistration observer 620 may recommend the user to push the wearabledevice back up after detecting slippage of the wearable device (such asdown the user's nasal bridge), may recommend that the user adjust someadjustable component of the wearable device (e.g., as described hereinin connection with FIGS. 15A and 15B), etc.

Example of a Registration Coordinate System

FIGS. 12A-12B illustrate an example eye position coordinate system,which may be used for defining three-dimensional positions of a user'sleft and right eyes relative to the display of the wearable systemdescribed herein. As examples, the coordinate system may include axis x,y, and z. Axis z of the coordinate system may correspond to depth, suchthe distance between the plane a user's eyes lie in and the plane thatdisplay 220 lies in (e.g., the direction normal to the plane of thefront of a user's face). Axis x of the coordinate system may correspondto a left-right direction, such as the distance between the users leftand right eyes. Axis y of the coordinate system may correspond to anup-down direction, which may be a vertical direction when the user isupright.

FIG. 12A illustrates a side view of a user's eye 1200 and a displaysurface 1202 (which may be a part of display 220 of FIG. 2), while FIG.12B illustrates a top down view of the user's eye 1200 and the displaysurface 1202. Display surface 1202 may be located in front of the user'seyes and may output image light to the user's eyes. As an example,display surface 1202 may comprise one or more out-coupling lightelements, active or pixel display elements, and may be part of a stackof waveguides, such as stacked waveguide assembly 480 of FIG. 4. In someembodiments, the display surface 1202 may be planar. In some otherembodiments, the display surface 1202 may have other topologies (e.g.,be curved). It will be appreciated that the display surface 1202 may bea physical surface of the display, or simply a plane or other imaginarysurface from which image light is understood to propagate from thedisplay 220 to the user's eyes.

As shown in FIG. 12A, the user's eye 1200 may have an actual position1204 offset from a nominal position 1206 and the display surface 1202may be at position 1214. FIG. 12A also illustrates the corneal apex 1212of the user's eye 1200. The user's line of sight (e.g., their opticaland/or visual axis) may be substantially along the line between theactual position 1204 and the corneal apex 1212. As shown in FIGS. 12Aand 12B, the actual position 1204 may be offset from the nominalposition 1206 by an z-offset 1210, a y-offset 1208, and an x-offset1209. The nominal position 1206 may represent a preferred position(sometimes referred to as a design position, which may be generallycentered within a desired volume) for the user's eye 1200 with respectto the display surface 1202. As the user's eye 1200 moves away from thenominal position 1206, the performance of display surface 1202 may bedegraded, as discussed herein in connection with FIG. 14 for example.

In addition, it will be appreciated that the default position for arender camera may be the nominal position 1206. As discussed herein, thedisplay system may be configured to render content from the perspectiveof the imaginary render camera. As a result, various parameters of therender camera, e.g., focal length, may impact the appearance of contentprovided to the user. For example, the focal length may determine themagnification and size of virtual content presented to the user. Thus,different focal lengths may be associated with different depth planes.

In some embodiments, the lens of the render camera may be positioned atthe nominal position 1206 as a default, with the nominal position 1206assumed to correspond to the center of rotation, which may be understoodto be the point 1204 in this example. However, offsets of the center ofrotation 1204 from the nominal position 1206 may cause undesirableviewer discomfort. For example, it will be appreciated thatmagnification errors can occur on a per-eye basis and virtual contentmay appear larger or smaller than intended. In one scenario, if thefocal length of the render camera is shorter than expected (e.g., as aresult of the center of rotation of the user's eye being positionedbehind the nominal position, but without compensating for thisdisplacement or offset in render space), then virtual content may appearsmaller than intended. Similarly, if the focal length of the rendercamera is longer than expected (e.g., as a result of the center ofrotation of the user's eye being positioned in front the nominalposition, but without compensating for this displacement or offset inrender space), then virtual content may appear larger than intended. Ifsuch magnification errors are different for each eye (e.g., as a resultof the center of rotation of the one eye being positioned behind thenominal position and the center of rotation of the user's other eyebeing positioned in front of the nominal position, without propercompensation of these offsets in render space), the perceived size ofthe same virtual object may differ from eye-to-eye. This difference insize may cause the user to experience some level of discomfort (e.g.,potential eye strain and/or headache from trying to reconcile binocularsize discrepancies).

In some embodiments, the focal length of the render camera may bedetermined based upon the z-axis offset between the default position1206 (the position assumed for the center of rotation) and the actualposition of the center of rotation 1204. For example, if the center ofrotation is positioned behind the nominal position, then the focallength of the render camera may be reduced (e.g., reduced by the offsetamount). On the other hand, if the center of rotation is positioned infront of the nominal position, then the focal length may be increased(e.g., increased by the offset amount).

In addition, in some embodiments, the focal length of the render cameramay also be calculated based upon the depth plane being used by thesystem. For example, in some embodiments, the optics of the rendercamera may be assumed to follow the thin lens equation (1/o+1/i=1/f),where o is the object distance (e.g., the depth plane on which contentis being presented), i is a constant (e.g. the distance from the centerof rotation to the user's retina), and f is the focal length. Asdiscussed herein, the depth plane on which content is presented has aset distance from the user. As a result, since the quantities o and iare known, the focal length may be determined by solving for f. In someimplementations, render camera focal length adjustments may be performedin connection with one or more operations described herein, such as step1170, as described above with reference to FIG. 11, and step 1610, asdescribed in further detail below with reference to FIG. 16. Examples ofadditional render camera adjustment schemes that may be employed by oneor more of the systems described herein are provided in U.S. PatentProv. App. 62/618,559, entitled “EYE CENTER OF ROTATION DETERMINATION,DEPTH PLANE SELECTION, AND RENDER CAMERA POSITIONING IN DISPLAY SYSTEMS”filed on Jan. 17, 2018 and U.S. Patent Prov. App. 62/702,849, entitled“EYE CENTER OF ROTATION DETERMINATION, DEPTH PLANE SELECTION, AND RENDERCAMERA POSITIONING IN DISPLAY SYSTEMS” and filed on Jul. 24, 2018, bothof which are incorporated by reference herein in their entirety.

With continued reference to FIG. 12A, it will be appreciated that apoint or volume associated with the user's eye 1200 may be used torepresent the position of the user's eye in analyses of registrationherein. The representative point or volume may be any point or volumeassociated with the eye 1200, and preferably is consistently used. Forexample, the point or volume may be on or in the eye 1200, or may bedisposed away from the eye 1200. In some embodiments, the point orvolume is the center of rotation of the eye 1200. The center of rotationmay be determined as described herein and may have advantages forsimplifying the registration analyses, since it is roughly symmetricallydisposed on the various axes within the eye 1200 and allows a singledisplay registration volume aligned with the optical axis to be utilizedfor the analyses.

FIG. 12A also illustrates that the display surface 1202 may be centeredbelow the user's horizon (as seen along the y-axis when the user islooking straight ahead, with their optical axis parallel to the ground)and may be tilted (with respect to the y-axis). In particular, thedisplay surface 1202 may be disposed somewhat below the user's horizonsuch that the user would have to look downward, at approximately theangle 1216, to look at the center of the display surface 1202, when theeye 1200 is at position 1206. This may facilitate a more natural andcomfortable interaction with the display surface 1202, particularly whenviewing content rendered at shorter depths (or distances from the user),as users may be more comfortable viewing content below their horizonthan above their horizon. Additionally, display surface 1202 may betilted, such as at angle 1218 (with respect to the y-axis) such that,when the user is looking at the center of the display surface 1202(e.g., looking slightly below the user's horizon), the display surface1202 is generally perpendicular to the user's line of sight. In at leastsome embodiments, the display surface 1202 may also be shifted left orright (e.g., along the x-axis) relative to the nominal position of theuser's eye. As an example, a left-eye display surface may be shiftedright-wards and a right-eye display surface may be shifted left-wards(e.g., display surfaces 1202 may be shifted towards each other) suchthat the user's lines of sight hits the centers of the display surfaceswhen focused at some distance less than infinity, which may increaseuser comfort during typical usage on the wearable device.

Example of a Display Registration Volume

FIGS. 13A-13B illustrate an example display registration volume 1302 a.The display registration volume 1302 a may represent the spatial volumein which the eye 1200 is positioned so as to receive image light fromthe display device. In some embodiments, a center of rotation of auser's eye is preferably located so that the eye registers, or receives,image information from the display device. In some embodiments, when thecenter of rotation of the user's eyes is located within the displayregistration volume 1302 a, the user is able to see the entirety of theimage outputted by the display device with high brightness uniformity.For example, as described herein, a properly registered display mayallow an image to be seen across about 80% or more, about 85% or more,about 90% or more, or about 95% or more of the field of view of thedisplay, with a brightness uniformity of 80% or more, about 85% or more,about 90% or more, or about 95% or more. In other words, a display witha “good” registration (as determined by module 772 of FIG. 7C, as anexample) may have a brightness uniformity of 90% or more, a display witha “marginal” registration may have a brightness uniformity of 80% ormore, and a display with a “failed” registration may have a brightnessuniformity of less than 80%.

As also described herein, the center of rotation 1204 may serve as aconvenient reference point for referring to and determining thethree-dimensional position of the user's eyes. The center of rotation ofeach of a user's eyes may be determined using the techniques describedherein, such as by walking back from the center of curvature of a corneato the center of rotation (CoR) along the user's optical axis. However,in general, any desired reference point associated with a user's eye maybe utilized in the processes and systems described herein. The displayregistration volume 1203 may represent the volume of space in whichdisplay surface 1202 is able to operate at near full potential (e.g.,without significant degradation, of the type described in connectionwith FIGS. 15A and 15B, of the performance of the display surface 1202).If the user's eye (e.g., the center of rotation 1204 of the user's eye)is not within the registration volume 1302 a, the user may experiencedegraded performance and some or all of the content provided by displaysurface 1202 may be partially dimmed or completely invisible to theuser.

As shown in FIG. 13A, the registration volume 1302 a may have the shapeof a frustum, which is the portion of a pyramid remaining after itsupper portion has been cut off, typically by a plane parallel to itsbase. In other words, the registration volume 1302 a may be larger alongthe x axis and the y axis (see, e.g., FIGS. 12A and 12B) when the user'seye is closer to the display surface 1202 and may be smaller along the xand y axis when the user's eye is further from the display surface 1202.A frustum is an example of a truncation in which the shearing plane(e.g., the line at which a portion of the original shape is cut off) isparallel to the base of the volume. In general, the registration volumesuch as volume 1302 a may take the shape of a volume truncated in anymanner, such as by one or more non-parallel shearing planes (e.g., suchas shown in FIG. 13B) or by one or more non-planar shearings.

The dimensions of the registration volume may depend on the specificimplementation of display surface 1202 and other elements of thewearable system. As an example, FIG. 13B illustrates that a registrationvolume 1302 b that may be angled with respect to the display surface1202. In the example of FIG. 13B, the portion of the registration volume1302 b closest to display surface 1202 may be angled away from thedisplay surface 1202, such that as the user's eye moves vertically (inthe y direction) at the front of the volume (the z position closest tothe display surface 1202), the user's eye would need to move away fromthe display surface (along the z axis) to remain inside the registrationvolume 1302 b. In some embodiments, the shape of the registration volume1302 b may be based on the capabilities of an eye tracking system, whichmay not be able to track the user's eyes outside the angled volume 1302b of FIG. 13B.

The dimensions and shape of the registration volume may also depend uponthe properties of the various parts of display 220, which may includedisplay surface 1202. As an example, display 220 may be a light fielddisplay with one or more waveguides (which may be stacked and which canprovide multiple vergence cues to the user), in-coupling elements thatreceive light from an image injection device and couple the light intothe waveguides, light distributing elements (sometimes referred to asorthogonal pupil expanders (OPE's)) disposed on the waveguide(s) thatdistribute light to out-coupling elements, and out-coupling elements(sometimes referred to as exit pupil expanders (EPE's)) that directlight towards a viewer's eye. In some embodiments, as noted herein, thedisplay surface 1202 is a surface or portion of a surface from whichlight with image information is output from the display system to formimages in the eye of the user. For example, the display surface 1202 maybe the area on the waveguide surface defined by the out-couplingelements or EPE's, and the perimeter of the display surface 1202 is theperimeter of the area defined by the out-coupling elements or EPE's.Further examples and details of light field displays and the componentsof such displays are also described in connection with at least FIGS.9A-9C U.S. Provisional Patent Application No. 62/642,761, filed Mar. 14,2018, which is incorporated by reference herein in its entirety.

In some embodiments, the x dimensions of registration volume 1302 a mayspan approximately 3.0 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 4.7 mm, 5.0mm, 5.5 mm, or 6.0 mm; or may be less than 3.0 mm; or more than 6.0 mmalong the back of the volume (e.g., at the largest distances along thez-axis from the display surface). Similarly, the y dimensions of theregistration volume 1302 a may span approximately 2.5 mm, 3.0 mm, 3.5mm, 3.9 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, or 6.0 mm; or may be lessthan 2.5 mm; or more than 6.0 mm along the back of the volume. Atnominal x and y positions, the z dimensions of the registration volume1302 a may span approximately 7.0 mm, 7.5 mm, 8.0 mm, 8.5 mm, 9.0 mm,9.5 mm, 10.0 mm, 10.5 mm, or 11.0 mm; or less than 7.0 mm; or more than11.0 mm. The x and y dimensions may be larger at the front of thevolume. As examples, the x and y dimensions of the registration volumeat the front of the volume may be approximately 7.0 mm, 7.5 mm, 8.0 mm,8.5 mm, 8.9 mm, 9.0 mm, 9.5 mm, 10.0 mm, 10.0 mm, 10.5 mm, 11.0 mm, 11.4mm, 11.5 mm, 12.0 mm, or 12.5 mm; or less than 7.0 mm; or more than 12.5mm. As specific examples, the dimensions of the registration volume mayinclude a z-dimension of approximately 9 mm; an x-dimension ofapproximately 4.7 mm at the back of the volume and approximately 11.4 mmat the front of the volume; and a y-dimension of approximately 3.9 mm atthe back of the volume and approximately 8.9 mm at the front of thevolume.

In at least some embodiments, there may be multiple registrationvolumes, such as volumes 1302 b and 1304, each of which is associatedwith a different minimum level of display performance. As an example,volume 1304 of FIG. 13B may be smaller than volume 1302 and mayrepresent the volume in which the user perceives all of the contentprovided by display surface 1202 at 100% brightness uniformity, whereasthe larger volume 1302 b may represent the volume in which the userperceives at least 90% of the content provided by display surface 1202at 100% brightness uniformity. Thus, in some embodiments, the displaysystem may be configured to determine whether the user's eye is within aregistration, or viewing, volume of the display, and/or may beconfigured to determine whether the user's eye is within a thresholddistance from the registration volume. For example, in some embodiments,the smaller volume 1304 may be considered to be the baselineregistration volume or viewing volume, and the boundaries of the largervolume 1302 b may be considered to demarcate an acceptable thresholddistance from the registration volume. In some embodiments, if thedisplay system determines that the position of the eye is more than thethreshold distance outside of the viewing volume of the display system,the display system may be configured to provide feedback to the userindicating that the display and the eye are not properly registered foroutput and/or to take actions to mitigate display degradation caused bymisregistration, as discussed herein.

In some embodiments, the display registration volume may be determinedat least in part based on an application that is currently running orwill be run on the system. For example, a larger display registrationvolume (e.g., volume 1302 b) may be employed by the display system whenrunning an application in which only a portion of the field of view isutilized for displaying virtual content, such as a reading-basedapplication in which the reading material may only occupy a portion(e.g., a central portion) of the display's field of view. As a result,the loss, due to misregistration, of the ability of the user to perceiveimage content at the periphery of the field of view may not beperceptible when running such a reading-based application, since theapplication may not present content at the periphery. As a result, thelarger display registration volume may be utilized to, e.g., reduceunnecessary notifications to the user regarding misregistration whensuch image registration may not impact the content presented by theapplication being run on the display system. Similarly, in anotherexample, a larger display registration volume (e.g., volume 1302 b) maybe employed by the display system when running an application in whichthe head-mounted display is expected to shift relative to the user'seyes, such as an exercise-oriented application or another applicationthat requires a relatively high-level of user engagement and/or physicalactivity. In such applications, a notification regarding misregistrationmay be considered, e.g., distracting, or otherwise detract from the userexperience; providing a larger display registration volume reduces thelikelihood that the display system will generate such a modification forthe user. In some other embodiments, a smaller display registrationvolume may be utilized (e.g., volume 1304) when running applications inwhich it is desired to provide content across the full field of view ofthe display or at peripheral portions of the field of view. Suchapplications may include immersive gaming applications in which contentis displayed across the entirety of the display's field of view. In someimplementations, a display registration volume may be determined basedon other factors including user preferences, user vision prescription,operating conditions of the system, and the like.

FIGS. 13C and 13D illustrate an example display registration volume,configured to use the center of rotation of an eye as a reference pointindicative of the position of the eye, relative to the eye of a user anda display surface. In particular, FIG. 13C illustrates an examplepositioning of a display registration volume, such as registrationvolume 1302 b, within a user's eye 1200. In the example of FIG. 13C, thecenter of rotation 1204 of the eye 1200 is roughly centered within theregistration volume 1302 b. Additionally, the registration volume 1302 bis illustrated with example dimensions of approximately 9 mm of depthand, at the mid-point of the depth axis, approximately 3.5 mm of widthand 3 mm of height. As discussed herein, the dimensions of registrationvolume may vary and may be related to the properties of variouscomponents of the wearable system. FIG. 13C also illustrates an eyestructure 1340, which may be the lens or pupil of eye 1200.

FIG. 13D shows a larger context, in which the user's eye 1200 isgenerally positioned within registration volume 1302 b and is lookingthrough display surface 1202 at virtual content 1350. As discussedherein, virtual content such as the virtual content 1350 may be providedto the user with vergence and accommodation cues associated with greaterdepths than the depth of the display surface 1202. In other words, thevirtual content 1350 may appear to the user with eye 1200 to be at agreater distance from the user than the display 1202. Such anarrangement is illustrated in the example of FIG. 13D.

With continued reference to FIG. 13D, it will be appreciated that thedisplay registration volume 1302 b may be an imaginary volume havingboundaries defined by a projection from the perimeter of the displaysurface 1202 to a point inside the eye 1200. For example, the projectionmay define a pyramid and the display registration volume 1302 b may be afrustum of that pyramid. Thus, the cross-sectional shape of the displayregistration volume 1302 b, along planes facing the display surface 1202on the optical axis, is similar to the shape made out by the perimeterof the display surface 1202. For example, as illustrated, where thedisplay surface 1202 is square, the cross-sectional shape of the displayregistration volume 1302 b is also square. In addition, as alsoillustrated, where the center of the display surface 1202 is below theuser's horizon, a frustum may also be slanted such that a center of thefront of the display registration volume 1302 b is also below the user'shorizon. It will be appreciated that, in some embodiments, the relevantperimeter of the display surface 1202 is the perimeter of the area ofthe display over which image light or display content is outputted. Theboundaries of the display registration volume 1302 b may be defined inthe same coordinate system in which various features, such as the centerof rotation 1204, of the eye 1200 are mapped, thereby allowingcomparisons between the display registration volume 1302 b and thesevarious features.

In some embodiments, the center of rotation 1204 of the eye is centeredwithin the frustum that defines the display registration volume 1302 b.It will be appreciated, however, that the nominal placement of center ofrotation 1204 of the eye and/or the overall shape of the frustum may bedetermined empirically or selected using criteria other than projectionfrom the display surface 1202 so that the display system is able toproperly register the display and to provide accurate feedback regardingthe quality of the registration and the levels of registration that maybe acceptable even if not ideal.

Examples of a Display Performance at Various Registration Positions

FIG. 14 illustrates how the performance of display surface 1202 may varywith the position of the user's eye 1200. As illustrated, light raysfrom the display surface 1202 may be directed to the eye at an angle,such that light rays from the edges of the display surface 1202propagate inwards towards the eye 1200. Thus, the cone 1202′ representsa cone of light outputted by the display surface 1202 to the eye 1200 toform an image.

Consequently, as the display surface 1202 shifts relative to eye 1200,the exit pupils of pixels corresponding to a respective portion of thefield of view do not reach the retina of eye 1200, and the image appearsto dim at those portions of the field of view. The positions 1204 a,1204 b, 1204 c, and 1204 d of the center of rotation of the eye areeffectively shifted relative to the idealized position 1204′ of thecenter of rotation; movement of the display surface 1202 relative to theeye 1200 may cause the center of rotation of the eye to possibly moveoutside of the display registration volumes 1302 a, 1304, 1302 b (FIGS.13A and 13B) for the display surface 1202. As discussed herein, thedisplay registration volumes may be tied to the display surface 1202,e.g., the display registration volumes may be defined by projectionsfrom the display surface 1202. Consequently, as the display surface 1202moves relative to the eye 1200, so do the display registration volumes1302 a, 1302 b (FIGS. 13A and 13B). FIG. 14 illustrates variouspositions (e.g., positions 1204 a, 1204 b, 1204 c, and 1204 d) of thecenter of rotation of a user's eyes, the relative position of a displaysurface 1202, and representations (e.g., representations 1400 a, 1400 b,1400 c, and 1400 d) of how the content provided by display surface 1202would be perceived by the user at each of the various positions.

In example 1400 a, the center of rotation of the user's eye may be atposition 1204 a, which may be centered within a registration volume suchas registration volume 1300 b (e.g., a volume in which image quality ishigh due to the eye 1200 receiving on its retina nearly all of the imagelight outputted by the display surface 1202). Representation 1400 a mayrepresent the user's perception (or view) of the content provided bydisplay surface 1202, when the user's eye is at position 1204 a. Asshown by representation 1400 a, the luminance for substantially all ofthe content across the display surface 1202 is uniform and may be at ornear full brightness levels.

In example 1400 b, the center of rotation of the user's eye may be atposition 1204 b, which may be outside a preferred display registrationvolume such as volume 1304 (FIG. 13B) but inside a secondaryregistration volume such as volume 1302 b (e.g., a volume in whichdisplay performance is only slightly degraded). Representation 1400 bmay represent the user's perception (or view) of the content provided bydisplay surface 1202, when the center of rotation of the user's eye isat position 1204 b. As shown by representation 1400 b, the portion 1402of the image along the right side of the display surface 1202 may have aperceived reduced brightness (e.g., a 50% brightness) due tomisregistration of the user's eye relative to the display surface 1202.

In example 1400 c, the center of rotation of the user's eye may be atposition 1204 c, which may be outside (or on the outside edge of) asecond registration volume such as volume 1302 b (FIG. 13B).Representation 1400 c may represent the user's perception (or view) ofthe content provided by display surface 1202, when the center ofrotation of the user's eye is at position 1204 c. As shown byrepresentation 1400 c, a portion 1406 along the edge of the displayedimage user's perception may appear completely (or nearly completely)dimmed and thus not seen by the user due to misregistration. Inarrangements in which some pixels of the display are below a perceivedluminance level, the display may provide a reduced field of view (e.g.,the user may not be able to perceive the full field of view the displayis otherwise capable of presenting). Additionally, there may be a bandor portion 1404 of the image having progressively reduced brightnessbetween the dark portion 1406 and the rest of the representation.

In example 1400 d, the center of rotation of the user's eye may be atposition 1204 d, which may be well outside the desired registrationvolumes. Representation 1400 d may represent the user's perception (orview) of the content provided by display surface 1202, when the centerof rotation of the user's eye is at position 1204 d. As shown byrepresentation 1400 d, large portions 1410 of the image may appearcompletely (or nearly completely) dark to the user and a substantialportion 1408 of the image may appear dimmed, due to the significantmisregistration.

As discussed herein, it will be appreciated that the display system maybe configured to increase the light output or perceived brightness ofportions of the field of view of the display which undergo dimming dueto misregistration. For example, upon determining that there ismisregistration, as discussed herein, the display system may provide anotification in the form of a flag or instructions for the display toincrease the amount of light outputted to the user for pixels expectedto undergo dimming due to misregistration. For example, in example 1400b, pixels representing image information in portion 1402 may have theirperceived brightness boosted to mitigate reductions in perceivedbrightness expected from misregistration.

It will be appreciated that the ability to boost brightness tocompensate for dimming may diminish with high levels of misregistration.For example, in example 1400 d, the area 1410 may be dark due to the eye1200 not receiving any light from pixels in those areas. Consequently,while boosting brightness may mitigate dimming due to misregistration inthe portion 1402 (example 1400 b), boosting brightness may not be ableto mitigate dimming in portions 1410 (example 1400 d) of the displaywhere misregistration prevents the eye from receiving light at all. Theportion 1410 is larger than the portion 14 to and, as an approximation,the size of the portion expected to be dimmed may be indicative ofwhether or not boosting brightness is effective; that is, if the size ofthe portion (e.g., the number pixels) expected to be dimmed issufficiently large, then, in some embodiments, it may be assumed thatthe misregistration is sufficiently great that boosting brightness willnot be effective for most of those pixels. As a result, in someembodiments, the display system may be configured to compare the numberpixels in the portions expected to be dimmed, and if that number exceedsa threshold, then provide feedback to the user indicating that thedisplay and the eye are not properly registered.

Example of Interchangeable Fit Pieces for Wearable Systems

FIGS. 15A and 15B show exploded perspective views of the wearable system220, which may include interchangeable fit pieces. In particular, FIG.15A illustrates how the wearable system 200 may include interchangeableback padding such as pads 1500 a, 1500 b, and 1500 c; while FIG. 15Billustrates how the system 200 may include interchangeable forehead padssuch as pad 1502 and interchangeable nose bridge pads such as pad 1504.These interchangeable pads may be used to adjust the fit of the wearablesystem 200 for individual users, whom may have varying anatomicalattributes (e.g., how the display 220 and frame 230 fit for variousdifferent users). As examples, users with relatively small heads maybenefit from attaching relatively large back pads 1500 a, 1500 b, and1500 c to the frame 230, while users with relatively large heads mayobtain better results (e.g., better optical performance and stability ofthe frame 300 on their head) by attaching relatively small back pads, oreven omitting the back pads. Similarly, users with prominent nosesand/or foreheads may benefit from smaller forehead pads 1502 and/or nosebridge pads 1504; while users with less prominent noses and/or foreheadsmay benefit from larger forehead pads 1502 and/or nose bridge pads 1504.These are merely illustrative examples and, in general, determining theset of interchangeable pads that result in the best fit for anyparticular user may be complex. As described herein, the display systemmay display a notification to the user indicating that a differentinterchangeable fit piece may be desirable to provide properregistration of the display to the user.

With reference to FIG. 15A, the wearable system may include one or morehousing openings 1510. The housing openings 1510 may be openings inframe 230 and may, if desired, optionally include lenses or otherstructures, such as optically transmissive structures for mechanicalprotection of the waveguides of the display. Lenses in housing openings1510 may be clear (e.g., fully or nearly fully transparent) or may bepartially opaque (e.g., in order to reduce the level of ambient lightthat passes through the openings 1510). The openings in frame 230, whileillustrated in FIG. 15A as being approximately circular, may have anydesired shape.

Example Processes of Observing Device Registration

FIG. 16 is a process flow diagram of an example method 1600 forobserving device registration and providing feedback on registration orcompensation for misregistration in a wearable device. The method 1600may be performed by the wearable systems described herein. Embodimentsof the method 1600 may be used by the wearable system to providefeedback on registration (i.e., fit of the wearable device to the user)based on data from an eye tracking system and to adjust a display toattempt to compensate for fit errors (e.g., misregistration).

At block 1602, the wearable system may obtain fit tolerances. The fittolerances may include information associated with display registrationvolumes such as volumes 1302 a, 1302 b, or 1304. In particular, the fittolerances may include information associated with nominal (e.g.,normal) positions of the user's eyes relative to the wearable device andmay include information associated with how variances from the nominalpositions impact device performance. As one example, the fit tolerancesmay include information on a range of nominal positions for which thewearable device is able to interface with a user at least a certaindesired amount of performance (e.g., with no more than 50% dimming onany pixel in a display).

At block 1604, the wearable system may obtain registration data. Theregistration data may include spatial relationships between variouscomponents of the wearable system and associated portions of the user.As examples, the registration data may include one or more of thethree-dimensional positions of a user's left eye relative to a left-eyedisplay of the wearable system; 3D positions of the user's right eyerelative to a right-eye display; and 3D positions of the user's earsrelative to audio outputs (e.g., speakers, headphones, headsets, etc.)of the wearable system. The wearable system may obtain registration datausing any suitable mechanisms. As an example, the wearable system maycapture images of a user's eye or eyes using eye-tracking cameras 324 ofthe type shown in FIG. 3 (or other cameras, which may or may not beinward-facing cameras) to determine the relative positions of the user'seyes and the wearable system. As other examples, the wearable system mayinclude depth sensors, pressure sensors, temperature sensors, lightsensors, audio sensors, or other sensors to measure or obtainregistration data such as the position of the wearable device relativeto a user.

At block 1606, the wearable system may determine fit characteristics. Asan example, the wearable system may determine whether the user's lefteye lies within a left-eye registration volume (such as one of volumes1302 a, 1302 b, or 1304 for the left eye) and whether the user's righteye lies within a right-eye registration volume (such as one of volumes1302 a, 1302 b, or 1304 for the right eye). Block 1606 may also involvedetermining how far the user's eyes (or other body parts) are from theirnominal positions. As an example, the wearable system, in block 1606,may determine that at least one of the user's eyes is outside of itsrespective the display registration volume, by how much and in whichdirection the user's eyes are outside of their display registrationvolumes. Information on the direction and magnitude of themisregistration (e.g., the distance between the registration volumes ornominal positions and the actual positions of the user's eyes or otherbody part) may be beneficially utilized in blocks 1608 and 1610.

At block 1608, the wearable system may provide a user (or some otherentity) with feedback on the fit characteristics determined in block1608. As an example, if the wearable system determines in block 1606that the wearable device is too low relative to the user's eyes, thewearable system may provide the user, at block 1608, with a notificationsuggesting that the user utilize an appropriate nose bridge pad 1504(e.g., to add a nose bridge pad if none were previously attached or toswap out an existing nose bridge pad for a larger or taller nose bridgepad). Conversely, if the wearable device determines it is too highrelative to the user's eyes, the system may provide a suggestion to theuser to use a smaller nose bridge pad or remove the pad altogether (ifdesigned to be wearable without a pad). As other examples, the wearablesystem may provide the user with feedback suggesting a change toforehead pads such as pad 1502, back pads such as pads 1500 a-1500 c, achange to other adjustable components of the wearable system, a changeto how the user is wearing the wearable system (e.g., instructions tomove or rotate the system in a particular direction relative to theuser). In general, user feedback may be generated based on theposition(s) of the user's eye(s) relative to the display or othermetrics such as the visible image portions identified by the system. Asan example, when the system determines that the user's eye is above theregistration volume, the system may recommend to the user that the userpush the wearable device upwards along the bridge of their nose in orderto correct the misregistration.

User feedback may be provided using any suitable device. As examples,user feedback may be provided via video presented by a display in thewearable device or an external display or via audio presented by thewearable device or by an external device. In various embodiments, thewearable device may provide an interactive guide for assisting the useris obtaining proper registration in a relatively intuitive manner. As anexample, the wearable device could display two virtual targets, onerepresentative of the position of the user's eyes and the otherrepresentative of the nominal registration position. Then, as the usermoves the wearable device around and adjusts its fit, the user canperceive how their adjustments impact registration and the user canquickly and intuitively achieve proper registration.

In arrangements in which user feedback is provided by an output device,such as a display, that is part of the wearable device, the wearabledevice may provide the user feedback in a manner that ensures the useris able to perceive the feedback. Consider, as an example,representation 1400 d of FIG. 14. In such an example, the wearablesystem may move user feedback into portion of the displayed image thatis perceived by the user e.g., the left-half of the display, as opposedto the invisible right-half of the display in the example 1400 d of FIG.14.

In some embodiments, feedback of the type described herein may beprovided to a sale associate in a retail environment and the feedbackmay be communicated over a network to the sale associate's computer ormobile device.

At block 1608, the wearable system may adjust its outputs and inputs tocompensate for uncorrected fit errors. In some embodiments, block 1608may be performed only after a user has failed to correct fit errors inresponse to feedback. In other embodiments, block 1608 may be performeduntil a user corrects fit errors. In some embodiments, block 1608 may beperformed whenever the user decides to continue using the wearablesystem with fit errors. In some embodiments, block 1608 may be omitted.

As examples, the wearable system may adjust its outputs and inputs inblock 1608 by adjusting portions of a displayed image (e.g., tocompensate for misregistration-induced dimming, of the type shown inFIG. 14), by adjusting microphone inputs (e.g., boosting microphone gainwhen a user is too far from a microphone, or reducing microphone gainwhen the user is too close to the microphone), by adjusting speakeroutputs (e.g., boosting or dimming speaker volume when a user is tooclose or too far, respectively, from a speaker in the wearable device),etc. As one particular examples, the wearable system may selectivelyboost the luminance of portions of the image, such as portions 1402,1404, or 1408 of FIG. 14, in an attempt to reducemisregistration-induced dimming. In some other embodiments, the wearablesystem may recognize that certain portions of the image, such asportions 1406 or 1410 of FIG. 14. are not visible to the user and mayreduce light output in those regions to reduce energy consumption by thewearable system. For example, in configurations where different portionsof the image may have dedicated, selectively-activated light sources orportions of a light source, the one or more light sources or portions ofa light source associated with the unseen portions of the image may havetheir light output reduced or turned off.

Example of Identifying a Display Registration Volume

FIGS. 17A-17H illustrate views of light fields projected by a displayand how the intersections of the light fields may partly define adisplay registration volume. FIG. 18 illustrates a top-down view ofoverlapping light fields projected by a display and how theintersections of the light fields can partly define a displayregistration volume. As FIGS. 17A-17H and 18 illustrate, the size andshape of display registration volume can depend in part upon thegeometry of the display (which can be display 220 of FIG. 2) as well asthe angles at which out-coupled light propagates out of the display(e.g., out of the waveguide the display). It will be appreciated thatthe angles at which the light is output may define the FOV of thedisplay; larger angles relative to the normal provide a larger FOV. Insome embodiments, the display surface may output angles large enough toprovide a desired FOV.

FIGS. 17A-17H and 18 illustrate display 220, which can be a light fielddisplay including elements such as waveguide 1701, in-coupling elements1702, orthogonal pupil expanders (OPE's) 1704, and exit pupil expanders(EPE's) 1706 (which can form a display surface 1202, which is alsoillustrated in various other Figures herein including FIGS. 12A-14). Asan example, the in-coupling elements 1702 can receive light from animage source and couple the light into waveguide 1701. The waveguide1701 can convey the light to OPE's 1704, the OPEs 1704 may provide pupilexpansion and direct the light to EPE's 1706, and the EPE's 1706 (whichcan be provided on display surface 1202) provide further pupil expansionand convey the light to the user's eye(s). Further examples and detailsof light field displays and the components of such displays are alsodescribed in connection with at least FIGS. 9A-9C U.S. ProvisionalPatent Application No. 62/642,761, filed Mar. 14, 2018, which isincorporated by reference herein in its entirety.

FIG. 17A illustrates an example in which the display 220 is projectinglight 1710 associated with virtual image content at optical infinity andthe right-most region (e.g., right-most pixel) of the FOV of thedisplay. In contrast, FIG. 17B illustrates an example in which thedisplay 220 is projecting light 1712 associated with an object atoptical infinity and the left-most region (e.g., left-most pixel) of theFOV of the display. FIG. 17C illustrates the overlapping region 1714 ofthe light 1710 of FIG. 17A and the light 1712 of FIG. 17B. Region 1714may be a horizontal registration volume. In particular, when the user'seye is disposed within region 1714 of FIG. 17C, the user is able toperceive (e.g., display 220 is able to provide the user with light from)objects at both the right-most region of the FOV (as in FIG. 17A) andthe left-most region of the FOV (as in FIG. 17B).

FIGS. 17D-F illustrate examples similar to those of FIGS. 17A-17E,except in the vertical direction. In particular, FIG. 17D illustrates anexample in which the display 220 is projecting light 1716 associatedwith an object at optical infinity and the bottom-most region (e.g.,bottom-most pixel) of the FOV of the display, while FIG. 17E illustratesan example in which the display 220 is projecting light 1718 associatedwith an object at optical infinity and the top-most region (e.g.,bottom-most pixel) of the FOV of the display. Similarly, FIG. 17Fillustrates the overlapping region 1720 of the light 1716 of FIG. 17Dand the light 1718 of FIG. 17E. Region 1720 may be a verticalregistration volume. In particular, when the user's eye is disposedwithin region 1720 of FIG. 17F, the user is able to perceive (e.g.,display 220 is able to provide the user with light from) objects at boththe bottom-most region of the FOV (as in FIG. 17D) and the top-mostregion of the FOV (as in FIG. 17E).

FIGS. 17G and 17H illustrate the intersection (as region 1722) of theregions 1714 of FIG. 17C and the region 1720 of FIG. 17F. In particular,FIG. 17G illustrates the region 1722 in which light from objects at thefour corners of the FOV of display 220 overlaps. FIG. 17H illustratesjust the outline of region 1722. As should be apparent, when the user'seye is disposed within region 1722, the user is able to perceive (e.g.,display 220 is able to provide the user with light from) objectsanywhere within the FOV of the display. In some embodiments, theregistration volume of the display 220 may be understood to be a viewingvolume of the head-mounted display through which light representingevery pixel of virtual image content presented by the head-mounteddisplay is expected to pass.

In some embodiments, increasing the FOV of display 220 (horizontally,vertically, or a combination thereof) while holding other attributes(such as display size) constant may have the effect of shrinking therelevant registration volume (e.g., the horizontal volume 1714, thevertical volume 1720, or the combined registration volume 1722).Consider, as an example, FIGS. 17A-C and the horizontal FOV andregistration volume 1714. An increase in the horizontal FOV of display220 means light 1710 from objects on the right horizontal edge isprojected by display surface 1202 (e.g., EPE's 1706) at a sharper angle(e.g., a greater angle from normal to display surface 1202). Similarly,light 1712 from objects on the left horizontal edge is projected at asharper angle. Thus, in the perspective of FIG. 17C, the apex of thehorizontal registration volume 1714 moves toward display surface 1202with increases in horizontal FOV, thereby shrinking volume 1714. Similarconsiderations may apply in some embodiments to the vertical FOV and thevertical registration volume, as well as the overall FOV and overallregistration volume.

FIG. 18 shows a top-down view of display 220 including display surface1202, which may have a rectangular shape and a particular FOV, as wellas light rays produced by the display. In general, the registrationvolume of the display 220 of FIG. 18 may be the volume 1802, whichappears triangular in the top-down perspective of FIG. 18. The volume1802 may represent the volume where the various light fields formed bythe light shown in FIGS. 17A-17G overlap. If a user's eye is locatedoutside of volume 1802 (e.g., in volume 1804), it may be seen that lightof light fields from at least some portion of the display 220 would failto reach the user's eye, resulting in partial or complete dimming of aportion of the FOV.

It should be noted that a side-view of the display and registrationvolume would have much the same appearance (at least for a rectangulardisplay) as that shown in FIG. 18, although the illustrated dimension ofdisplay 220 would be the height of the display 220 rather than its widthand the illustrated FOV would be the vertical FOV rather than thehorizontal FOV shown in FIG. 18. Thus, the volume 1802 may actually havea somewhat pyramidal shape. In other embodiments, the display may havenon-rectangular shapes such as a circular shape, an elliptical shape, afree-form shape, or any other desired shape. In such embodiments, thecorresponding registration volume may be determined by projecting lightfields at the relevant FOV and identifying where those light fieldsintersect (which may correspond to volume 1802) and where the lightfields do not intersect (which may correspond to volume 1804).

As discussed herein, the “base” of the pyramid may be truncated (whichmay help to move the user's eyes away from the display such that theuser's eyelashes do not impact the display when properly registered) andthe “top” of the pyramid may also be truncated (which may be helpful inreducing the impacts of noise in the location determination of theuser's eyes, which might otherwise rapidly move into and out ofregistration at the “top” of a pyramidal shaped registration volume). Itwill be appreciated that the “top” is proximate the apex of the volume1802, and the base is proximate the waveguide 1701. When the user's eyesare located in regions 1804 outside of the registration volume 1802, theuser may perceive dimming of some or all of the pixels of display 220,as discussed herein (see, e.g. FIG. 14).

In general, the registration volume may be adjusted (e.g., truncated orotherwise reduced) in any number of ways for a variety of reasons. As anexample, the registration volume may be truncated such that the volumehas a minimum distance from display 220, to prevent the user's eyelashesor lids from impacting the display 220. Consequently, in someembodiments, the display system (e.g., processing electronics of thedisplay system) may be configured to determine whether the user's eyesare inside of the registration volume 1802 by, at least in part,determining whether one or both eyes are less than a minimum thresholddistance (e.g. a minimum allowable distance) from the display 220. If aneye is determined to be at less than the minimum threshold distance fromthe display, then the display system may interpret this result to meanthat the eye is outside of the registration volume 1802 and, thus, thedisplay and the eye are not properly registered. As a result, thedisplay system may provide feedback to the user indicating that theregistration is improper, and/or may be configured to take actions tomitigate display degradation caused by misregistration, as discussedherein. In some implementations, such a minimum threshold distance mayvary in one or more dimensions. For example, the minimum thresholddistance may linearly vary along the z-axis as a function of distancefrom the nominal position and/or the surface of the display.

In addition or as an alternative to determining whether the eye iswithin a minimum distance from the display 220, in some embodiments, thedisplay system (e.g., processing electronics of the display system) maybe configured to determine whether the user's eyes are inside of theregistration volume 1802 by, at least in part, determining whether oneor both eyes are more than a maximum threshold distance from the display220. It will be appreciated that the maximum threshold distance maycorrespond to the distance at which the “top” of the pyramid 1802 notedabove is truncated. If an eye is determined to be at more than themaximum threshold distance from the display, then the display system mayinterpret this result to mean that the eye is outside of theregistration volume 1802 and, thus, the display and the eye are notproperly registered. As a result, the display system may providefeedback to the user indicating that the registration is improper,and/or may be configured to take actions to mitigate display degradationcaused by misregistration, as discussed herein.

In addition or as an alternative to determining whether the eye iswithin a minimum distance and/or beyond a maximum distance from thedisplay 220, the wearable system may have an eye tracking system,including elements such as cameras 324 and light sources 326 of FIG. 6,which may only track the user's eyes if the user's eyes are within aneye tracking volume, which may not overlap exactly with the displayregistration volume. In some embodiments, the camera of the eye trackingsystem may have a field of view which encompasses the displayregistration volume. Thus, the display registration volume may beconsidered to be a subspace, or portion, of the camera's field of view.The display system may be configured to determine whether the user's eyeis within that subspace, or within a threshold distance from thatsubspace, when imaged by the camera. If the eye is within the subspaceor within a threshold distance from the subspace, then the displaysystem may interpret this result to mean that the eye is within thedisplay registration volume. If the eye is outside of the subspace oroutside a threshold distance from the subject, then the display systemmay interpret this result to mean that the eye is outside of the displayregistration volume. If the display system determines that the eye isoutside of the display registration volume, the display system may beconfigured to provide feedback to the user indicating that the displayand the eye are not properly registered for output, and/or may beconfigured to take actions to mitigate display degradation caused bymisregistration, as discussed herein.

Examples of a Housing Registration Volume and a System RegistrationVolume

FIG. 19A illustrates an example housing registration volume 1900. Lightfrom the ambient environment passes through the opening in the frame orhousing of the display to reach the user. It will be appreciated thatthe frame or housing for the display may block some ambient light, fromsome angles, from reaching the eyes of the user. As a result, analogousto the display registration volume, and the housing registration volume1900 may represent the spatial volume in which a user's eye ispositioned so as to receive light from the external environment to makeout the full field of view available through the housing or frame of thedisplay. In some embodiments, a center of rotation of a user's eye ispreferably located within the housing registration volume 1900 so thatthe eye receives light from the external environment at anglescorresponding to the full available field of view. In some embodiments,when the center of rotation of the user's eye is located within thehousing registration volume 1900, the user is able to see an acceptableportion of the world around them. Proper registration of the user's eyeto the wearable system (e.g., by providing the center of rotation withinthe housing registration volume 1900) may help to reduce the likelihoodthat the user will be unable to see obstacles in their paths, mayprovide users with a left and right fields-of-view that overlap tofacilitate binocular vision, and/or may provide a more comfortablevisual experience for users.

As shown in FIG. 19A, the housing registration volume 1900 may bepartially or wholly determined with reference to housing openings 1510,which may be openings (or lenses) in frame 230 of the wearable system aspreviously discussed in connection with FIG. 15A. The housingregistration volume 1900 may, as an example, have a cone-like shape witha base defined by the shape and size of the housing openings 1510.Portions of the cone-like shape nearest the housing openings 1510 andportions farthest from the housing openings 1510 may be truncated (e.g.,excluded from the housing registration volume 1900), which may help tomove the user's eyes away from the display and housing openings 1510such that the user's eyelashes do not impact the display when properlyregistered and may help reduce the impacts of noise in the locationdetermination of the user's eyes, which might otherwise rapidly moveinto and out of registration in the small volume at the “top” of acone-shaped registration volume. In some embodiments, the display systemmay be configured to determine whether the user's eyes (e.g., thecenters of rotation of the eyes) are within the housing registrationvolume 1900 and to provide notifications of misregistration if theuser's eyes are outside of the registration volume 1900.

FIG. 19B illustrates the display registration volume 1302 a of FIG. 13A(associated with display surface 1202) superimposed on the housingregistration volume 1900 of FIG. 1900 (associated with housing openings1510). In at least some embodiments, it may be desirable for the centerof rotation of a user's eye to be located within both the housingregistration volume 1900 of FIG. 19A and the display registration volumesuch as the display registration volume 1302 a of FIG. 13A (or any ofthe other display registration volumes discussed herein). When theuser's eye is located within both the housing and display registrationvolumes, the user may be able to receive image information from thedisplay device (with the full field of view provided by the displaydevice) while also be able to view the full field of view of theexternal environment provided by the housing.

FIG. 19C illustrates an example of a combined registration volume 1902,where every point in the combined registration volume 1902 lies withinboth the housing and display registration volumes (e.g., within displaceregistration volume 1302 a and housing registration volume 1900). Asshown in FIGS. 19B and 19C and in at least some embodiments, the displayregistration volume 1302 a may be generally smaller than the housingregistration volume 1900 (e.g., the housing registration volume 1900 mayonly be smaller at the corners of the display registration volume 1302a). In such embodiments, the combined registration volume 1902 may havea shape similar to a truncated pyramid having rounded corners, asillustrated in FIG. 19C. In some embodiments, the display system may beconfigured to determine whether the user's eyes (e.g., the centers ofrotation of the eyes) are within the housing registration volume 1900,the display registration volume 1204, or both the housing registrationvolume 1900 and the display registration volume 1204. If the user's eyesare outside the particular volume being analyzed, the display system maybe configured to provide notifications of misregistration if the user'seyes are outside of the registration volume being analyzed (e.g., thehousing registration volume 1900, the display registration volume 1204,or both the housing registration volume 1900, the display registrationvolume 1204).

For example, in some embodiments, the combined overlapping registrationvolume defined by the housing registration volume 1900 and the displayregistration volume 1204 may be analyzed to determine whether the user'seyes are within this combined registration volume. In some embodiments,this may be understood to be a portion or subspace of the registrationor viewing volume of the housing, which may also referred to as theouter housing. The display system may be configured to determine whetherthe user's eye is within this subspace (or an acceptable thresholddistance outside of the subspace). If the display system determines thatthe position of the eye is more than the threshold distance outside ofthe subspace of the viewing volume of the outer housing of the display,and then it may provide feedback to the user indicating that the displayand the eye are not properly registered.

Computer Vision to Detect Objects in Ambient Environment

As discussed above, the display system may be configured to detectobjects in or properties of the environment surrounding the user. Thedetection may be accomplished using a variety of techniques, includingvarious environmental sensors (e.g., cameras, audio sensors, temperaturesensors, etc.), as discussed herein.

In some embodiments, objects present in the environment may be detectedusing computer vision techniques. For example, as disclosed herein, thedisplay system's forward-facing camera may be configured to image theambient environment and the display system may be configured to performimage analysis on the images to determine the presence of objects in theambient environment. The display system may analyze the images acquiredby the outward-facing imaging system to perform scene reconstruction,event detection, video tracking, object recognition, object poseestimation, learning, indexing, motion estimation, or image restoration,etc. As other examples, the display system may be configured to performface and/or eye recognition to determine the presence and location offaces and/or human eyes in the user's field of view. One or morecomputer vision algorithms may be used to perform these tasks.Non-limiting examples of computer vision algorithms include:Scale-invariant feature transform (SIFT), speeded up robust features(SURF), oriented FAST and rotated BRIEF (ORB), binary robust invariantscalable keypoints (BRISK), fast retina keypoint (FREAK), Viola-Jonesalgorithm, Eigenfaces approach, Lucas-Kanade algorithm, Horn-Schunkalgorithm, Mean-shift algorithm, visual simultaneous location andmapping (vSLAM) techniques, a sequential Bayesian estimator (e.g.,Kalman filter, extended Kalman filter, etc.), bundle adjustment,Adaptive thresholding (and other thresholding techniques), IterativeClosest Point (ICP), Semi Global Matching (SGM), Semi Global BlockMatching (SGBM), Feature Point Histograms, various machine learningalgorithms (such as e.g., support vector machine, k-nearest neighborsalgorithm, Naive Bayes, neural network (including convolutional or deepneural networks), or other supervised/unsupervised models, etc.), and soforth.

One or more of these computer vision techniques may also be usedtogether with data acquired from other environmental sensors (such as,e.g., microphone) to detect and determine various properties of theobjects detected by the sensors.

As discussed herein, the objects in the ambient environment may bedetected based on one or more criteria. When the display system detectsthe presence or absence of the criteria in the ambient environment usinga computer vision algorithm or using data received from one or moresensor assemblies (which may or may not be part of the display system),the display system may then signal the presence of the object.

Machine Learning

A variety of machine learning algorithms may be used to learn toidentify the presence of objects in the ambient environment. Oncetrained, the machine learning algorithms may be stored by the displaysystem. Some examples of machine learning algorithms may includesupervised or non-supervised machine learning algorithms, includingregression algorithms (such as, for example, Ordinary Least SquaresRegression), instance-based algorithms (such as, for example, LearningVector Quantization), decision tree algorithms (such as, for example,classification and regression trees), Bayesian algorithms (such as, forexample, Naive Bayes), clustering algorithms (such as, for example,k-means clustering), association rule learning algorithms (such as, forexample, a-priori algorithms), artificial neural network algorithms(such as, for example, Perceptron), deep learning algorithms (such as,for example, Deep Boltzmann Machine, or deep neural network),dimensionality reduction algorithms (such as, for example, PrincipalComponent Analysis), ensemble algorithms (such as, for example, StackedGeneralization), and/or other machine learning algorithms. In someembodiments, individual models may be customized for individual datasets. For example, the wearable device may generate or store a basemodel. The base model may be used as a starting point to generateadditional models specific to a data type (e.g., a particular user), adata set (e.g., a set of additional images obtained), conditionalsituations, or other variations. In some embodiments, the display systemmay be configured to utilize a plurality of techniques to generatemodels for analysis of the aggregated data. Other techniques may includeusing pre-defined thresholds or data values.

The criteria for detecting an object may include one or more thresholdconditions. If the analysis of the data acquired by the environmentalsensor indicates that a threshold condition is passed, the displaysystem may provide a signal indicating the detection the presence of theobject in the ambient environment. The threshold condition may involve aquantitative and/or qualitative measure. For example, the thresholdcondition may include a score or a percentage associated with thelikelihood of the reflection and/or object being present in theenvironment. The display system may compare the score calculated fromthe environmental sensor's data with the threshold score. If the scoreis higher than the threshold level, the display system may detect thepresence of the reflection and/or object. In some other embodiments, thedisplay system may signal the presence of the object in the environmentif the score is lower than the threshold. In some embodiments, thethreshold condition may be determined based on the user's emotionalstate and/or the user's interactions with the ambient environment.

In some embodiments, the threshold conditions, the machine learningalgorithms, or the computer vision algorithms may be specialized for aspecific context. For example, in a diagnostic context, the computervision algorithm may be specialized to detect certain responses to thestimulus. As another example, the display system may execute facialrecognition algorithms and/or event tracing algorithms to sense theuser's reaction to a stimulus, as discussed herein.

It will be appreciated that each of the processes, methods, andalgorithms described herein and/or depicted in the figures may beembodied in, and fully or partially automated by, code modules executedby one or more physical computing systems, hardware computer processors,application-specific circuitry, and/or electronic hardware configured toexecute specific and particular computer instructions. For example,computing systems may include general purpose computers (e.g., servers)programmed with specific computer instructions or special purposecomputers, special purpose circuitry, and so forth. A code module may becompiled and linked into an executable program, installed in a dynamiclink library, or may be written in an interpreted programming language.In some embodiments, particular operations and methods may be performedby circuitry that is specific to a given function.

Further, certain embodiments of the functionality of the presentdisclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware or one or morephysical computing devices (utilizing appropriate specialized executableinstructions) may be necessary to perform the functionality, forexample, due to the volume or complexity of the calculations involved orto provide results substantially in real-time. For example, a video mayinclude many frames, with each frame having millions of pixels, andspecifically programmed computer hardware is necessary to process thevideo data to provide a desired image processing task or application ina commercially reasonable amount of time.

Code modules or any type of data may be stored on any type ofnon-transitory computer-readable medium, such as physical computerstorage including hard drives, solid state memory, random access memory(RAM), read only memory (ROM), optical disc, volatile or non-volatilestorage, combinations of the same and/or the like. In some embodiments,the non-transitory computer-readable medium may be part of one or moreof the local processing and data module (140), the remote processingmodule (150), and remote data repository (160). The methods and modules(or data) may also be transmitted as generated data signals (e.g., aspart of a carrier wave or other analog or digital propagated signal) ona variety of computer-readable transmission mediums, includingwireless-based and wired/cable-based mediums, and may take a variety offorms (e.g., as part of a single or multiplexed analog signal, or asmultiple discrete digital packets or frames). The results of thedisclosed processes or process steps may be stored, persistently orotherwise, in any type of non-transitory, tangible computer storage ormay be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities may be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto may be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe embodiments described herein is for illustrative purposes and shouldnot be understood as requiring such separation in all embodiments. Itshould be understood that the described program components, methods, andsystems may generally be integrated together in a single computerproduct or packaged into multiple computer products.

Other Considerations

Each of the processes, methods, and algorithms described herein and/ordepicted in the attached figures may be embodied in, and fully orpartially automated by, code modules executed by one or more physicalcomputing systems, hardware computer processors, application-specificcircuitry, and/or electronic hardware configured to execute specific andparticular computer instructions. For example, computing systems mayinclude general purpose computers (e.g., servers) programmed withspecific computer instructions or special purpose computers, specialpurpose circuitry, and so forth. A code module may be compiled andlinked into an executable program, installed in a dynamic link library,or may be written in an interpreted programming language. In someimplementations, particular operations and methods may be performed bycircuitry that is specific to a given function.

Further, certain implementations of the functionality of the presentdisclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware or one or morephysical computing devices (utilizing appropriate specialized executableinstructions) may be necessary to perform the functionality, forexample, due to the volume or complexity of the calculations involved orto provide results substantially in real-time. For example, animationsor video may include many frames, with each frame having millions ofpixels, and specifically programmed computer hardware is necessary toprocess the video data to provide a desired image processing task orapplication in a commercially reasonable amount of time.

Code modules or any type of data may be stored on any type ofnon-transitory computer-readable medium, such as physical computerstorage including hard drives, solid state memory, random access memory(RAM), read only memory (ROM), optical disc, volatile or non-volatilestorage, combinations of the same and/or the like. The methods andmodules (or data) may also be transmitted as generated data signals(e.g., as part of a carrier wave or other analog or digital propagatedsignal) on a variety of computer-readable transmission mediums,including wireless-based and wired/cable-based mediums, and may take avariety of forms (e.g., as part of a single or multiplexed analogsignal, or as multiple discrete digital packets or frames). The resultsof the disclosed processes or process steps may be stored, persistentlyor otherwise, in any type of non-transitory, tangible computer storageor may be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities may be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto may be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe implementations described herein is for illustrative purposes andshould not be understood as requiring such separation in allimplementations. It should be understood that the described programcomponents, methods, and systems may generally be integrated together ina single computer product or packaged into multiple computer products.Many implementation variations are possible.

The processes, methods, and systems may be implemented in a network (ordistributed) computing environment. Network environments includeenterprise-wide computer networks, intranets, local area networks (LAN),wide area networks (WAN), personal area networks (PAN), cloud computingnetworks, crowd-sourced computing networks, the Internet, and the WorldWide Web. The network may be a wired or a wireless network or any othertype of communication network.

The systems and methods of the disclosure each have several innovativeaspects, no single one of which is solely responsible or required forthe desirable attributes disclosed herein. The various features andprocesses described above may be used independently of one another, ormay be combined in various ways. All possible combinations andsubcombinations are intended to fall within the scope of thisdisclosure. Various modifications to the implementations described inthis disclosure may be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

Certain features that are described in this specification in the contextof separate implementations also may be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also may be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orsteps. Thus, such conditional language is not generally intended toimply that features, elements and/or steps are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or steps are included or are to beperformed in any particular embodiment. The terms “comprising,”“including,” “having,” and the like are synonymous and are usedinclusively, in an open-ended fashion, and do not exclude additionalelements, features, acts, operations, and so forth. Also, the term “or”is used in its inclusive sense (and not in its exclusive sense) so thatwhen used, for example, to connect a list of elements, the term “or”means one, some, or all of the elements in the list. In addition, thearticles “a,” “an,” and “the” as used in this application and theappended claims are to be construed to mean “one or more” or “at leastone” unless specified otherwise.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Similarly, while operations may be depicted in the drawings in aparticular order, it is to be recognized that such operations need notbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flowchart. However, other operations that arenot depicted may be incorporated in the example methods and processesthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously, or betweenany of the illustrated operations. Additionally, the operations may berearranged or reordered in other implementations. In certaincircumstances, multitasking and parallel processing may be advantageous.Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems may generally be integratedtogether in a single software product or packaged into multiple softwareproducts. Additionally, other implementations are within the scope ofthe following claims. In some cases, the actions recited in the claimsmay be performed in a different order and still achieve desirableresults.

What is claimed is:
 1. A method for evaluating registration of virtualimage content from a head-mounted display system by a user's eye,wherein the head-mounted display system comprises one or moreeye-tracking cameras and at least one interchangeable fit piece, themethod comprising: determining a position of the eye based on images ofthe eye obtained with the one or more eye-tracking cameras; determiningwhether the position of the eye is within a display registration volumeof the head-mounted display system, wherein the display registrationvolume is an imaginary volume associated with proper fit of thehead-mounted display system relative to the user's eye; and providing anotification based on a determination that the position of the eye isoutside the display registration volume, where the notificationindicates at least that the display and the eye are not properlyregistered.
 2. The method of claim 1, wherein providing the notificationcomprises providing instructions causing the display system to boost abrightness of a plurality of pixels of the display relative to otherpixels of the display, wherein the plurality of pixels with boostedbrightness comprise pixels expected to undergo perceived dimming underimproper registration.
 3. The method of claim 1, wherein providing thenotification comprises providing feedback to the user that thehead-mounted display system is not properly adjusted to fit the user andproviding a suggestion to the user to swap out a currently-installedinterchangeable fit piece for another interchangeable fit piece.
 4. Themethod of claim 1, wherein the head-mounted display system is configuredto provide a first field of view when the position of the eye is insidethe display registration volume and a second field of view when theposition of the eye is outside the display registration volume, andfurther comprising changing a field of view of the head-mounted displaysystem from the first field of view to the second field of view when theposition of the eye is outside the display registration volume.
 5. Themethod of claim 4, wherein providing the notification comprisesdisplaying feedback to the user within the second field of view.
 6. Themethod of claim 1, wherein the head-mounted display system comprises aneye-tracking camera, wherein determining the position of the eyecomprises utilizing the eye-tracking camera to image the eye of theuser.
 7. The method of claim 6, wherein the position of the eye is aposition of a center of rotation of the eye, and further comprisingcalculating the center of rotation of the eye based upon imaging of theeye by the eye-tracking camera.
 8. The method of claim 6, furthercomprising continuously tracking the center of rotation of the eye whilethe head-mounted display system is in use and notifying the user whenthe center of rotation of the eye moves outside of the displayregistration volume.
 9. The method of claim 1, wherein the head-mounteddisplay system is configured to project light into the eye to displayvirtual image content in a field of view of the user, and furthercomprising displaying an indication that the display system is properlyfitted, wherein displaying the indication comprises providing feedbackto the user that the head-mounted display system is positioned such thatthe user's eye is within the display registration volume.
 10. The methodof claim 1, wherein, when the eye of the user is not within the displayregistration volume, dimming at least some pixels of the head-mounteddisplay system, wherein the dimmed pixels correspond to portions of apossible field of view of the display system that are outside of areduced field of view associated with the eye being outside the displayregistration volume.
 11. A method for evaluating registration of virtualimage content from a head-mounted display system by an eye of a user,wherein the head-mounted display system comprises a display disposed ona frame supported on a head of the user, the method comprising:determining a position of the eye based on images of the eye obtainedwith one or more eye-tracking cameras attached to the frame; determiningwhether the position of the eye is more than a first threshold distanceoutside of a viewing volume of the head-mounted display system; and inresponse to determining that the position of the eye is more than thefirst threshold distance outside of the viewing volume of thehead-mounted display system, providing feedback to the user indicatingthat the display and the eye are not properly registered.
 12. The methodof claim 11, wherein determining whether the position of the eye is morethan a first threshold distance outside of the viewing volume comprises:determining whether the position of the eye is less than a secondthreshold distance from the head-mounted display system; and in responseto a determination that the position of the eye is less than the secondthreshold distance from the head-mounted display system, providing thefeedback to the user indicating that the display and the eye are notproperly registered.
 13. The method of claim 11, further comprisingobtaining a fit tolerance, wherein the fit tolerance comprisesinformation associated with changes in registration of the virtual imagecontent caused by variances of the user's eyes from a nominal positionrelative to the display system.
 14. The method of claim 11, furthercomprising obtaining registration data, wherein obtaining theregistration data comprises determining a spatial relationship betweenthe display system and the user's eye.
 15. The method of claim 11,further comprising: identifying an application running on the displaysystem; and determining the first threshold distance based on theidentified application.
 16. A method for evaluating registration ofvirtual image content from a head-mounted display system by an eye of auser, wherein the head-mounted display system comprises a frame and ahead-mounted display and at least one interchangeable fit piece attachedto the frame, the method comprising: determining whether light projectedby the head-mounted display is properly registered by the eye of theuser, wherein the display is configured to project light into the user'seye to display the virtual image content with different amounts ofwavefront divergence corresponding to different depth planes; andproviding feedback to the user if the light projected by thehead-mounted display is determined to not be properly registered,wherein the feedback comprises a suggestion to the user to swap out acurrently-installed interchangeable fit piece for anotherinterchangeable fit piece.
 17. The method of claim 16, wherein the atleast one interchangeable fit piece comprises an interchangeable nosebridge pad configured to adjust a fit between the frame and a nosebridge of the user.
 18. The method of claim 17, further comprisingdetermining that the user's eye is above a display registration volumeof the head-mounted display system, wherein the display registrationvolume is an imaginary volume associated with proper fit of thehead-mounted display system relative to the user's eye, and whereinproviding the feedback to the user comprises prompting the user toinstall a larger nose bridge pad.
 19. The method of claim 16, whereinthe at least one interchangeable fit piece comprises an interchangeableforehead pad configured to adjust a fit of the frame and a forehead ofthe user.
 20. The method of claim 16, wherein the at least oneinterchangeable fit piece comprises an interchangeable back padconfigured to adjust a fit of the frame and a back of the head of theuser.